and contains 96 teeth. This fitting must be very carefully managed, or it will look very unsightly when finished. The wheel itself must, of course, be cut in a separate chuck made for the purpose, and when it is fitted to its place it may be removed and the nose, Fig. 1, cut down to the size of that on the mandril, as all the same chucks may be used if necessary on the dome chuck as well as the mandril. Having the wheel fitted into its place, the tangent-screw must be now fitted. This is made of steel, and before cutting out the bearing into which it is fitted, the top cap should be fitted on, and the two screws got into their places. We now come to that part which necessitates great care and a proper tool, as we have to cut out a recess between the two bearings for the screw itself. To do this properly a tool must be either made, or at all events, obtained somehow. It consists simply of a small piece of steel turned to the desired size of the recess, and made into a cutter. It is a thing very easily done, and may be either cut with a cutter, in conjunction with a horizontal cutting-frame, or it can be filed out into sufficient number of teeth to effect its purpose. It will be observed that the screw is not visible, and consequently no dirt can ger to its working parts. The tangent-wheel is held in its proper place by a screw with large head and thin steel washer, as seen in engraving. The washer is fitted on a square filed on the pin of tangent-wheel. There is little more to be said upon the construction of this tool. If used a great deal, it is a good plan to have what is termed a transfer chuck for the purpose of placing the work truly upon either the nose of the mandril or of the domechuck-it is a great convenience, and saves all chance of the work being in any way out of truth. The engravings will give what further instructions may be required, so I will not occupy more space upon this subject. has succeeded in obtaining a vacuum of visable to increase the capacity to double, 1-390 millionth, he must, one would think, as small spheres make the probable errors have obtained as nearly perfect a vacuum as large. The gauge-tube dips direct into it is reasonable to imagine possible. That mercury in a cylinder, which can be raised stage is reached, it may be observed, when and lowered at pleasure, and thus enable the leakage of the apparatus is equal to the the experimenter to graduate the pressure amount of air that can be removed in a given to a nicety. By the use of a cylinder filled time, and although a vacuum of about 1-400 with mercury, instead of the usual indiamillionth was once observed in Prof. Rood's rubber tubing, small bubbles of air are preexperiments, such a degree as that would not vented from entering the gauge along with be maintained for many seconds. Without the mercury. All the tubing is supported a number of diagrams, it is impossible to at a distance of rather more than 2in. from make clear the actual arrangements adopted the woodwork by means of adjustable supby him, but the principle can be readily un- ports and clamps, the object being to faciliderstood, and applied in various ways. In tate heating with a Bunsen burner without the apparatus used by Edison, illustrated on risk of burning the wood; but where the p. 117, Vol. XXXII., we have a complicated glass is of necessity fixed closer, the wood arrangement of tubes and bottles, with stop- is protected with metal or coated with a cocks, bulbs, &c., but in Prof. Rood's, stop-solution of alum. The tubes, of course, cocks and grease are dispensed with, a must be properly annealed, which Prof. movable column of mercury being employed Rood effects by exposing them in heavy iron where it is desirable to have the facilities tubes to about the temperature of melting usually afforded by a stopcock. The reser-zinc for five hours, and then allowing an voir containing the mercury is an ordinary hour or two for the cooling process. So far inverted bell-glass, with a diameter of he has not met with an accident, although 100mm., and a height of double the diameter, drops of cold mercury have frequently fallen the mouth of which is closed by a cork on portions of the glass heated considerably carrying the tube and painted with a flexible above 212° Fahr. The cement used for cement. The tube enters the reservoir to luting and for joining the tubes is made by the extent of about 40mm., but just above melting Burgundy pitch with from three to the cork, which rests on a shelf and supports four per cent. of guttapercha. It should, the reservoir, it carries a piece of sheet-iron, when cold, be so hard as to resist the imshaped like a watch glass, and with its con-pression of the finger-nail. It is applied by vex side towards the cork. This cup-shaped heating the parts to be joined and then piece of iron, which is closely cemented to touching them with a fragment of the cold the tube, prevents the small air-bubbles which cement, which runs in and forms a joint creep up the tube from finding their way to which is transparent, and which can be its mouth, and is probably a not unimportant examined with a lens for the colours of thin part of the apparatus. The flow of mer-plates which always precede a leak. Prof. cury is regulated by means of a steel rod and Rood has had such joints in use for two cylinder connected to a lever attached to months at a time without a leak making its the board which closes the upper end of the appearance, and no appreciable amount of reservoir. The lower end of the steel vapour is yielded by the resinous compound, cylinder is filled up with a piece of pure which, however, is melted several times before rubber, which, after a little use, controls the it is used. For drying material, he prefers flow of mercury accurately. When the caustic potash that has been fused just mercury leaves the reservoir it falls into the before it is introduced into the drying tube. vacuum bulb, where it parts with most of During the exhaustion experiments the OBTAINING AND MEASURING VERY its air and moisture, and passes along a bent caustic potash can be heated nearly to the melting point, but if actually fused in the drying tube the glass invariably cracks. The various parts of the apparatus are kept hot by moving a Bunsen burner to and fro close to them; and at first starting, bubbles, mainly of vapour of water, are observed for fully a quarter of an hour. Without this precaution of heating, a higher vacuum than 1-25 millionth was found impossible; while constant using of the pump and gauge was found to gradually eliminate the air. One of the most important elements in the production of high vacua is leakage, which after the air is detached from the walls of the pump becomes and remains nearly constant. Thus the average of a number of experiments which had a duration ranging from eighteen hours to seven days shows that the pump leaked 001266 of a cubic mm. per hour, the pressure being_760 mm. One quarter of this leakage Prof. Rood says occurs at the top of the column of mercury; but the total leakage is four times as great when the pump is in action as when it is in a state of rest. The leakage of a plain Sprengel pump without stopcocks, and arranged as far as possible like Prof. Rood's, was for a mean of four experiments 06180 cubic mm. per hour, and the highest exhaustion ever obtained was only 1-5 millionth. HIGH VACUA. tube to the junction with the fall-tube. The arrangement of this part is, according to F TOR several purposes nowadays a simple Prof. Rood, by no means a matter of indifmethod of obtaining very high vacua ference, for the tube leading from the bulb is a desideratum of the physicist for re- should fall for some little distance and then searches on radiant matter, which Mr. turn up to the point of junction where the Crookes has introduced, as much as for experi- drops of mercury are broken off, in such a ments with incandescent carbons for the manner that a horizontal line drawn from the electric light, which that scientist has also proper level of the mercury in the bulb been making recently. Geissler's and passes through the point where the drops of Sprengel's pumps are well known, and we mercury fall off. The diameter of the gave or p. 117, Vol. XXXII., a combination, vacuum bulb is 27mm., the length of the inremarkable for its complexity, which Edison clined tube from it 150mm., and that of the is reported to have used in obtaining a rise to the fall tube 45mm., the junction vacuum in his incandescent electric lamps. being made with a good curve. The bore of The ordinary Sprengel pump, even in un- the tubes is about the same as that of the skilled hands, will produce a vacuum of fall tube, 1.78mm.; but it does not appear 1-5 millionth, but some time ago Mr. Crookes that any special merit attaches to these diobtained a vacuum of 1-20 millionth (see p. mensions: The fall-tube has a length of 639, Vol. XXIX.), and it was then thought 310mm. when it bends out and returns that a much higher vacuum would be im- sharply with a good loop, and then conpossible of attainment. By modification of tinues for a further length of 815mm. These the apparatus, which is based on the principle bends form a fluid valve preventing the return of the Sprengel pump-the flow of mercury of air into the pump, and the play of the in tubes-much higher vacua have been mercury in them greatly facilitates the pasobtained, especially by Prof. Ogden N. sage of the air downwards. The top of the Rod, Professor of Physics in Columbia mercury column representing the existing College, U.S. With a modified form of barometric pressure should be about 25mm. Sprengel he obtains easily vacua of 1-100 below the bends when the pump is in action, millionth, and has reached the 1-390 mil- a point which is easily regulated by means lionth without arriving at the limit of the of an adjustable shelf, which supports the Sixteen experiments made with possible action of his apparatus. The latter tube into which the fall-tube dips. For the improved pump arranged in groups of is fully described in a recent number of the measuring, Prof. Rood uses a modification four gave a mean of 1-74,853,449 with a Amers in Journal of Science, and assuming of McLeod's gauge, the tube containing the probable error, with reference to four means, that no error has been made in estimating the compressed air having a diameter of 1.35mm., of 2-28 per cent. of the quantity involved. degree of vacuum it is certain that the results and being closed at its upper extremity by A higher vacuum measured in the same way obtained by Prof. Rood are remarkable con- a glass rod, which is cemented in place. gave a grand mean of 1-178,411,934 with a sidering the simplicity and inexpensiveness The object of this is to obtain the compressed probable error of 5.42 per cent. Five readof the appliances employed. The 1-20 air in the form of a cylinder, and to allow ings at still higher exhaustions gave a mean millionth of an atmosphere corresponds to of the cleansing of the tube when necessary. of 1-381,100,000 with a probable error of the 1-100th of an inch in a barometrical The capacity of the gauge-sphere was that 10:36 per cent. of the quantity involved. column three miles high; so, if Prof. Rood due to a diameter of 60mm; but it is ad-Without using potash, but taking care to at once = The two central columns in Table B show that remove all vapour of water which collects proximate dispersive power, caloulated from the length spectra of various media. This will first in the bends by means of a Bunsen burner, mean indices. Sir J. Herschel refers all the media be shown for the distance C G 100, and Prof. Rood finds it practical to obtain to one standard of dispersion, viz., that given secondly, when BH equals the same number. vacua as high as 1-50 millionth which by a prism of water. Thus, if x represents the The following table gives the number of parts dispersive power of water for the lines B and contained between any two colour-lines. It is stamps his improved pump as the best appliance of its kind. With, or 0394, then that of another substance for constructed by the rule of simple proportion: the assistance of caustic potash, vacua as m and n thus for medium No. 1, C G = 96 and C D = 19, the same lines is (mx + nx2), where are co-efficients calculated for that substance. therefore we say as 96: 100: 19: (required high as 1-100 millionth are easily reached, Coddington gives a table of Herschel's co-effi- value of CD) =20 (very nearly); and so on and, as mentioned above, the extraordinary cients for the ten media contained in Fraun- throughout the list. degree of exhaustion represented by 1-390 hofer's list, which I subjoin; but I am unable millionth, has been frequently obtained to state by what process they were determined. without exhausting the capabilities of the Both the co-efficients are positive. pump. An illustrated description of the HERSCHEL'S TABLE OF earlier form will be found on p. 561. No, 804, showing the vacuum bulb and the branch leading to the fall tube, with the bend in the latter; but so far as the former is concerned, it requires modification, as it is essential that the bend entering the falltube should be in a horizontal line with the level of the mercury in the bulb. It will be gathered from what we have said that the apparatus is really as simple as it is efficient. ON THE IRRATIONALITY OF THE By "ORDERIC VITAL." HE following is a table of the various T differences the names of the substances are not repeated, but each horizontal line of numEbers, belongs to the medium occupying the same position in the foregoing list. The distance between any two lines, occupies the column to which is prefixed the letters denoting those lines. There is also given the arithmetical mean of the values of C and G, and B and H for each medium, and the dispersive power corresponding thereto. This latter term is, of course, obtained by dividing their difference by their mean value. Water the width of the spaces D E and EF is nearly constant for all the media; but that B C and CD diminish and F G and G H increase as the disTHE COEFFICIENTS OF persive power becomes greater. The signification DISPERSIVE POWER. of this table will be better understood if the quantities be represented in the form of a diagram. The columns are numbered according to the order of the media in the foregoing tables. Medium. Solution of Potash Crown Glass, No. 9 Flint Glass, No. 30 ግዜ. 1.00000 0.99626 1'06149 0 87374 0.88419 0.90131 1:29013 1*37026 1.37578 1.4258 n. 0.00000 4:58639 2 49199 The first part of the diagram on next page shows the position of the lines, when C and G are made to coincide; and the second when BH are so adjusted. In this latter part it is unnecessary to give the full list, as the five media selected are sufficient to serve as examples of the rest. With regard to the first series of media, let us examine the effect produced when No. 1 and No. 3 are used to form an achromatic combination. For No. 1 the distance B C is 8.33, but for When two prisms are so adjusted as to balance No. 3 it is only 6; hence the separation caused each other's dispersion, it is evident that the by the first is not wholly counteracted by the spectrum produced by the second must be equal, second, so that there is some red colour uncomor approximately equal, and opposite to that bined. Also, at the other extreme, there is a produced by the first, so that the rays separated portion of the violet outstanding; the combinaby the one may be combined by the other. It is, tion of these two extreme colours produces a therefore, necessary to determine what positions purple or wine-coloured fringe on the left hand the various lines will occupy in spectra of equal of the image. Similarly at the places D, E, and length. If these were the same for two media if there are portions of the yellow, green, and of different refractive powers, such a combina-blue rays uncombined, and these three form a tion could be made to refract light without dispersion; but it will be seen that this cannot be accomplished. When the extreme lines are made coincident, the interior lines are not so; and conversely, if two interior lines coincide, the extremes do not agree, so that there will be scattered colour in each case. We can determine by calculation what colours will not be wholly combined. coloured space from C to G is divided into 100 parts; then we can easily compare the positions, The last two columns in Table A give the ap- which the several lines will occupy, in equal green fringe on the right-hand side. In like the list, and combine it with the first, the same manner, if we take any medium lower down on fringes of colour appear, but varying in distinctness according to the difference in position of the colour lines. These appearances indicate, generally, that the dispersions are approximately balanced; for they are produced opposition; but such a combination is really when equal-length spectra are arranged in slightly under-corrected, because, though C and G are united, the three interior colours are a little displaced. Let us now try the effect of lengthening the spectrum produced by the more dispersive medium. Referring as before to the diagrams Nos. 1 and 3; if we lengthen spectrum No. 3, still keeping the Cline coincident, the lines D, E, and Fare brought nearly into the required place; but line G is displaced, so that an indigo or blue fringe would appear. This is termed over-correction, and is, I believe, often found in object-glasses of German manufacture. Which of these two characteristic appearances is considered to produce the best chromatic correction is a question that probably some of the readers of this journal may feel disposed to answer. In matters of this kind, we cannot be far wrong in following Sir John Herschel, and he was, I believe, in favour of an under-corrected objective. The second half of the diagram shows the different effect produced by combining another pair of lines. It will be observed that the difference in the positions of the colour-lines is much greater than in the preceding case, and the fringes will be correspondingly larger. Hence, it is obvious that the two lines which are combined should not be extreme lines as B and H, but rather those belonging to the more illuminating colours, such as C and G, or D and F. If we combine C and G, we get the image under-corrected; but if D and F, it will be overcorrected. In connection with medium No. 3, we may observe that it possesses properties different from any other in the list. Generally an increase in dispersive power accompanies an increase in refractive power, but in this case it is otherwise. Turpentine possesses a higher dispersive power than crown glass, although its refractive index is much less; and it contracts both the extreme lines of the spectrum. It would, therefore, seem that with two such media as Nos. 1 and 3, it would be an advantage to over-correct the image, as by so doing both the extreme and the middle lines would be brought nearly to agreement. But in the case of crown and flintglass, by altering the middle lines, the extremities, already over-corrected, are rendered more so. The preceding diagram gives some indica A DIAGRAM SHOWING THE DISTANCES BETWEEN THE COLOUR LINES IN EQUAL-LENGTH SPECTRA. H H 1. 4. 6. 8. 9. tion of the kinds of glass which leave the least outstanding colour. Among the first ten, the best effect would seem to be obtained by combining No. 6 with either No. 9 or No. 10; and among Chance's glass, soft crown and light flint appear to give the least secondary spectrum. (To be continued.) THE ORGAN AND HOW TO MAKE IT.-XIV. BY J. DRESSER. The Action-Work. HE action-work is the movement connecting trackers, levers, squares, and rollers, variously attached and applied to suit the requirements of the particular organ. A sticker is either round or square in section, and about a quarter of an inch thick; it is generally found on the tailend of the keys, where it pushes up the end of a lever or a square. A tracker is also a thin strip of some light wood, generally pine; it is sometimes round, at other times square, but more generally flat, about three-eighths by one-eighth of an inch; its action is to pull down either a roller-arm or a pallet. Levers or backfalls are generally made of mahogany or other hard wood; they vary in length from a few inches to two or three feet, and the size is generally one and a half inches wide and a quarter inch thick; these levers are usually let into a grooved rail, and fixed in that by a wire through the middle of the lever, the wire forming a centre for the lever to work on. This hole is generally bushed or lined with cloth to prevent noise in working, and, difficult as it may, at first sight, appear, to line a hole an eighth of an inch in diameter, it is in reality an extremely easy affair cut a strip of fine broad-cloth, say, the remains of an old coat, rather over a quarter inch wide, and ten or twelve inches long, cut one end to a point, very similar to a steel pen, put the point through the hole and draw the cloth through; it will take the form of the hole and completely line it; touch the cloth with glue where it is to remain in the hole, then out the cloth off neat and olean on each side. In amall, one-manual organs the action is very simple, and consists of the keys, stickers, and backfalls, as shown in Fig. 1; the pressing down of a key throws up the further end of it and pushes up the sticker, this pushes up one end of the lever; the other end being, consequently, depressed, pulls the pallet down and allows the wind to enter the pipe. If the pallets were the same size and distance apart as the koys, the backfalls would simply be straight lovers; but in practice it is very seldom so, and various plans are adopted to overcome that dittioulty The most usual plan is the fanframe, in which the levers spread out at the pallek-end, while at the other end they are keys; Fig. 2 shows such an ally, some of the bass notes end of the soundboard ance; the number is usually six for small organs, and the pipes so transferred are the alternate notes of the lowest octave-thus, CC, DD, &c., are on the left-hand or bass side, and CC sharp, DD sharp, FF &c., are on the right-hand or treble side; when this plan is adopted there are six more levers or backfalls beyond the range of the keys on the treble side; the motion to these levers is carried by a roller, which is of such a length that one arm is exactly over the end of the key, and the other arm is under the lever, Fig. 3. FIC.I. made, as shown in Fig. 7 by the dotted line, a piece of tough veneer, such as maple or beech, is firmly glued in. In making the last form of square, a piece of one and a half inch mahogany is cut off the end of a wide board as long as the length of the square, generally four inches; this is planed down to the shape of one arm of the square, Fig. 8, one end being bevelled to a true mitre; another piece is got out the same way, and the two are carefully glued together and well dried. Next make a sawcut every three-eighths of an inch, and let in a piece of veneer, according to Fig. 7; when all is dry, clean off the stuff, then saw the squares apart, taking care the sawcut is exactly between the veneers. Another plan is to leave the end of the block square, Fig. 6, and have each are cut off : this is easier for the general amateur arm together after the arms than the preceding, and equally as strong, but takes considerably more time; if two or three sets are required the bevel and tongue plan is best. Another, and still easier plan, which, perhaps, gives one the idea of cheapness and nasti ness, yet answers its purpose, is one good wood arm, and to form the other arm a short screwarm of wire is inserted. Fig. 9 will explain itself. Round stickers are run off with a bead-plane. quarter inch thick, then with a quarter inch bead-plane run a bead down each side of the board, as Fig. 10; the round bead will be so nearly detached that it will crack off; clean off the ridge with a smoothing plane, and then sandpaper, when a nice-looking round sticker will be the result. When flat or square stickers are required, a cutting gauge is used instead of a bead-plane, and they are cleaned off with either the smoothing or trying-plane. After the stickers are cut to the exact length, a wire is inserted at each end, and projects two inches. This goes through a small hole in the end of the square or backfall at one end and a similar hole in the key. A small circular washer of cloth is put over the wire, to prevent rattling by the end of the key and sticker touching each other. Before going further it may be advisable to | Get a clean piece of best pine, and plane it to a more fully explain the different parts, and how they are made. When a keyboard is fixed, the stickers are generally round, unless a lever coupler to a second manual is used; then the stickers are flat either half-way up or the full length. When a keyboard slides out, the stickers must be oblong in section at the lower end, even if they are rounded further up, as they then work through a register or guide rail to keep them in position when the keys are moved. Fig. 4 shows the end of a fixed manual with stickers to a backfall at A, and to a square at B. Squares are to an organ-builder what bell-cranks are to a bell-hanger-they change the line of motion from a horizontal to a vertical, or from a straight to right or left as required. Squares are made of any hard wood, but mahogany is generally used; Trackers are long thin slips of pine, and of sometimes they are cut out of one piece of board and shaped like Fig. 5, at other times they are any length from 10 or 12in. to as many feet. A made out of two pieces and halved together as piece of clean sound pine is planed up and cut shown by the dotted lines in Fig. 6, and fre-off to the required length, and the trackers cut quently are mitred together, and a sawcut being off with a cutting gauge, seven or eight should be cut to the inch. A tapped wire is generally tied on to one end and sometimes to both, or a wire is looped on according to requirement. The way the wire is threaded in the tracker is shown by the thick black line in Fig. 11, and also at the other end a tapped wire ready for binding with thread. Coarse red carpet-thread is frequently used for this purpose, and after being wound on is washed over with glue; the wire loops are usually made of copper bell-wire. Tapped wires are about three and a half inches long, having a screw threaded about an inch and a half at one end; they are made either of bronze, tinned-iron, or brass-wire; the thread of the screw should be as coarse as possible, as the leather button is very likely to wear loose and slip on a fine thread. THE ACETATE OF SODA STOVE. TWO As soon as the water in the vessel A has been at all events, for as long as we require to possess brought up to the boiling-point the reservoirs Cit. Again: facilities for the harmonious blending which contain the soda salts are inserted in A of a dense background, with an under-exposed foreground (as in the case of this negative of my old friend," the Matterhorn ") are very ready to hand and use. When I throw the image upon the sensitive paper I have only to take a piece of board, with its upper edge cut in the direction of the outline of the upper edge of the nearer range of hills; to place this at the distance of about two inches from the sensitive sheet on the screen; to move it slightly while I expose the dense background of the subject for, say, five minutes; then to give three minutes more to the whole picture, and I obtain a satisfactory result. And then, too, here is something advantageous to be done with our thin negatives, provided they possess detail and are free from fog. A picture which is almost useless for ordinary printing will often give good results as the basis of an enlargement. I usually find that my photographic friends who deprecate enlargement of views are the very men who do most of their work at home, or in their own immediate neighbourhood. They do not, therefore, quite appreciate the exceeding advantage to a traveller through many lands of carrying with him a pocket quarter-plate lens, camera, and stand, and a few dozen of these small prepared plates in his port ta manteau. WO methods of utilising acetate of soda for warming purposes are before the public, the original invention of M. Ancelin, in which acetate of soda alone is used, and a modification until the salts contained in them are melted. The recently patented by Herr A. Nieske, a chemist reservoirs are then replaced in their former First of all, the lens. I have been told again and of Dresden. The former has been taken up by position between cylinder and mantle, and emit again that any good quarter-plate lens would the London and North-Western Railway Com- the heat they contain so gradually and equably answer my purpose; but I have never succeeded in pany, who have a license for 3,000 foot-warmers, that the filling even after a lapse of from ten to finding one which gave good definition to the but according to the statements made the inven- twelve hours is found to be warm. The cylinder edges without so much stopping down as to render tion of Herr Nieske is in some respects superior. or vessel A can be entirely removed from the it useless for the purpose. But the new rapid paper It appears that two of the soda salts are pecu- stove, and the reservoirs heated, or the soda puts another aspect upon the whole business; and liarly adapted to the purpose-viz., the salts contained in the same melted in any suitable we may stop our lenses down, and so get sharpness hyposulphite and the acetate. The first-named boiler or similar receptacle; or the vessel C can to our heart's content, without prolonging the exsalt has the property of melting easier than the be heated in any other suitable place. The posure unduly. The lens I am using to-night is the latter, consequently when the hyposulphite of cylindrical vessel A is for this purpose provided new combination by Dallmeyer, made expressly for use in the lantern. I am employing a wide stop, soda is mixed with acetate of soda the former with a projecting ring or flange, which lies on for the reason that I do not wish to occupy your prevents the latter from crystallising too rapidly; three supports or brackets, which also serve to time needlessly; but you will see that it gives The two salts combine and form a permanent support the reservoirs C. The evaporation of fairly good definitition up to the edges. The next filling, so that the reservoirs, vessels, or recep- the water in the vessel A prevents the air in obstacle in the way of the enlargement of quartertacles containing the same can be soldered down, the room becoming too dry. For foot-warmers plate negatives arises from the fact that the sciopand thus hermetically closed. Herr Nieske has tubing or pipes run through the filling so as to ticon and other lanterns which might be employed found it preferable to employ the following pro- attain a greater surface for the emission of for the purpose have condensers too small in diaportion of the salts, one part hyposulphite of warmth; such foot-warmers retain their warm-meter to give more than the centre of a view. These soda to ten parts acetate of soda. The reservoirs ing properties for about twelve hours. Stomach, obstacles were overcome in the apparatus I am exor receptacles are filled to about three parts full, chest, and other warmers can be employed with hibiting to-night. I shall not apologise for the roughness of the apparatus before you. No attempt and the lid soldered on. In order to prepare the same filling, and are adapted for employment has been made to conceal the clumsiness of its the reservoirs for employment they are placed in hospitals, sick-rooms, and such-like. The workmanship, for the very reason that you may see in boiling-water until the filling is melted; warmth emitted by these reservoirs is especially that an effective apparatus does not depend for its this is readily ascertained by shaking the beneficial to patients, as the heat remains usefulness upon skilful and careful make. reservoir or vessel, which can be modified in equable, continues for several hours, and is not form according to the purpose for which it is only agreeable but beneficial. Another application to which this class of warmth reservoir can be put is to place the same within a nickelled or other suitable ball, which can be easily carried in a muff, overcoat, &c., and can be held in the hand when skating, riding, driving, walking, and so on, in cold weather. They can also be most advantageously employed for artificial breeding apparatus or incubators, as the warmth remains continuously the same, and is therefore the best substitute for the natural warmth of the blood. used. Fig. 1 is a vertical section and Fig. 2 a F E A In the first place, here is an unmistakable biscuit box, placed on its side, with an aperture in the upper side, for the smoke chimney of a common paraffin lamp. I have cut from the centre of the bottom of the box a number of slits to the circumference of a circle. The triangular pieces so cut have been bent inwards as to their points, and thus a circular opening has been made to receive the condensers, which are supported on the triangular pieces tied together with wire. The condensers should be five inches in diameter (mine are four and three-quarter inches, and are not large enough) for enlargements from a quarter-plate. I have mounted this pair at home thus: Two circular pieces of halfinch deal were cut with the fret saw, and in each B horizontal section of a "stove" which is suited for employment in bedrooms, sick-rooms, offices, dwelling and other rooms. The stove is placed on three or more feet with castors, so as to enable it to be easily transported from one place to another. A is a vessel of cylindrical or other suitable form; B is a perforated mantle forming the outer walls of the stove. The reservoirs C, filled with the soda salts above named, are arranged between the vessel A and the perforated mantle B of the stove. They are of such size that they can be inserted in the central vessel A by means of their handles D. The stove is closed by the cap E and lid F, which can be readily removed. The water in the vessel A can be brought to a boiling point by means of a burner in connection with a gas-pipe. size.' My object in introducing this subject this evening is to endeavour to do something which may tend to clear away the main hindrances to the more general practice of a branch of photography which, quite as much as any other with which I am familiar, abundantly repays the workman for the toil and trouble he bestows upon his work. Now, with regard to the oft-repeated argument on the futility of taking small negatives of views for future enlargement, I am not without hope that I may show you, as the result of to-night's experiment, that this is nothing less than a photographic heresy. An enlarged landscape, when properly managed and produced, is, I think, both from the artistic and the photographic standpoints, "a thing of beauty which, thanks to the stability of the Morgan process, I verily believe may be "a joy for ever"; or, of these a round aperture was made with this tool, on one side of the wood, of the same diameter as that of the condenser, and on the other side somewhat smaller. These flat wooden rings hold the condensers firmly, two small pieces of wood or metal being screwed on to the upper surface of each, to prevent the condensers from slipping from their places. The two plano-convex condensers were then placed in position, their convex sides all but touching, and a strip of thick millboard was nailed to each deal ring, so as to form a strong and steady tube. The condensers being in position, a wooden cocoa box, three inches in depth, was sawn down to the size of the biscuit tin, and its side and end replaced. The lid had an aperture made in it with the fret saw to hold a quarter-plate negative, at the top and bottom of which metal holders are fixed. It was then fastened to the tin biscuit box in front of the condensers by means of screws. I I have cut a circular opening, opposite to the condensers, for the lens, and have made two tubes of millboard, each two inches long, the one sliding inside the other for focussing purposes. These were constructed in the same way as the condensers, by Sawing a couple of circular rings out of half-inch Mt. Whitney itself, probably the highest elevation of land in the Union, fronts the plains to the eastward with a perpendicular precipice 3,000ft. in sheer height, at the foot of which lies a more gradual slope of snow fields, giving place in turn to a similar slope of broken rock and debris, extending down into the canon, from which the foot-hills spring on either side. As to the exact height of Mt. Whitney, the calculations necessary to ascertain it have not yet been worked out, but it is somewhere between 14,400 and 15,000ft. deal-the one about aquarter of an inch wider in although we had read something of desert sand and HAVE already mentioned that there are a few diameter than the other. The larger one is screwed on to the cocoa box, and then a strip of millboard has been tacked round to form the outer tube. The other ring has a similar tube tacked upon it, and carries the flange of the lens. This, I think, completes the apparatus. The whole has been constracted with the view of enlarging a quarter-plate negative up to the size of a whole sheet of Morgan's paper, and the common paraffin lamp, with an inch and a-half wick, gives ample light for the purpose. I fasten the paper upon a drawing-board, by means of drawing-pins, and place it at a distance of three feet four inches from the lens. I recommend, for development, deal trays covered with two or three coats of varnish. Pour a pint of water into the tray and place the paper upon the surface of the water. It will now become flat, and, after a few tilts of the tray, the whole surface is thoroughly wetted and ready for the developer. I next pour into a beaker two ounces of a saturated solution of protosulphate of iron, and add six ounces of saturated oxalate of potash and one drachm of a ten-grain solution of bromide of potassium. The picture soon makes its appearance, and, when sufficiently developed, is well washed, fixed with hypo., thoroughly washed again, and dried, and may be mounted and framed at plea sure. PROF. LANGLEY'S EXPEDITION TO The instruments reached Lone Pine at last, and its annoying qualities, we never fully realised its penetrating power until we unpacked the instruments. On the way across the desert the sand had crept through every crack and joint in the boxes, and the instruments were covered with the fine, dry dust. We experienced great difficulty at Lone Pine on account of the intense beat. Under a simple glass cover in a blackened box the mercury rose in a common thermometer to 240 deg. Fahrenheit. It was necessary to carry on a part of the observations in a darkened tent, and the temperature in it rose 80 high that human nature could not endure it. cases of total colour-blindness, or of people who see nothing but form and light and shade, but these, and also blindness to violet, are of such rare occurrence, that practically they scarcely call for consideration. My chief business to-night is to discuss the bearing of red-blindness or of green. blindness either complete or incomplete, upon the fitness of the subjects of these defects to engage in certain industries, of which those which call for the recognition of railway and marine signals are the chief. If we take as an illustration, in the first instance, the state of an engine-driver who is completely red-blind, and who is called upon to govern the The negative we are using to-night is of even course of a locomotive in obedience to certain character, and we need not, therefore, mask any In a beautiful little valley, just above the timber coloured signals, which may be either red and portion of it during the exposure. Having focussed line on Mount Whitney, we established our sta-green alone, or white and red and green, in accord carefully, through a sheet of yellow glass, I hold tion, pitched our tents on the shore of a little ance with the regulations of different roads, we in my left hand a piece of cardboard with an aper- mountain lake, and turned a cow which we were find that the signals present to him differens ture of the required size, and place this about three luxurious enough to bring with us, out in the short by which, in many cases, he can tell them apart; inches from the lens, giving it a slight movement grass. It was already too late in the season to take but these differences are of brightness, or luminosy, that the edges of the vignette which it produces our heaviest apparatus to the summit, and the main and not of colour. From the white light he receive may be soft and graduated; then, with the right camp remains in this lofty valley, within a two the whole of its green and violet, the red being inst hand, I remove the yellow glass and commence the hours' climb of the peak by the "Devil's Ladder." to him, so that what he sees is a blue grey, com exposure. This will, of course, vary with the We climbed to the top of the mountain, which paratively feeble in brightness when contrasted density of the negative, and the quality and amount affords a view of some of the grandest mountain with the impression made by the same light upon of the light from the lamp. It may be readily as-scenery in the world. Sharp Gothic peaks spring normal eye. The green light will be removed st certained by exposing a preliminary slip of the from the waste of rocky foothills on every hand. farther from the brightness by reason of its prepaper in sections of a minute each. We shall Keeler's Needle, which was subsequently ascended, ponderance of green, and the red will only be require five minutes for our work this evening. towers to a height of about 14,000ft., and is no broader visible by means of the rays other than red which at the summit than this study table. Lying full the red glass transmits, and if nothing but red was length on the flat rock that crowns the peak, and transmitted, would be invisible altogether, so as to reaching out with the hand at one side, we dropped be what an Irishman might perhaps call a dark stones down into the chasm dividing it from the light. For practical purposes, however, we may neighbouring mountain. They fell fully three- omit the white lights from consideration, and may quarters of a mile before they touched the side of fix our attention only upon the red and green. Of the cliff and struck upon the granite rock so far these, the former, to a red-blind man, would seem below that no sound came back to our ears. darker than the latter; and this reflection would As to results, science must wait the completion be reversed in the case of a green-blind. We may of our calculations from the data obtained. The perfectly well suppose the colour-blind person, in general conclusion, however, is that the "golar either case, to be unconscious of his defects. He constant," or absolute amount of heat the earth has all his life been accustomed to interpret receives from the sun, is very much larger than that the phrase "a red light" as meaning somedetermined by Herschel and other previous ob- thing which presents to him a dim or isete servers. Further that the distribution of this heat illumination, and to interpret the phrase "a grea to the earth and its effect in producing all the light" as something which presents to him changes of climate, and its importance as affecting stronger or brighter illumination. By the help of all the interests of agriculture, depend on forces this distinction, he may pass an examination which which are now, for the first time, becoming fully is inadequately conducted, and he may drive has known. The immediate consequences of this in its engine for long periods without accident or ma application to practical interests will probably be take. But the point at issue is that he is compelled der expediat large in this forthcoming account of and that his the expedition to be published by the Government. relative brightness only; and that his judgment Among incidental attainments of more strictly upon this relative brightness is liable to be mused scientific interest may be mentioned that conclu- by accidental circumstances. Anything which is sions have been reached that will probably be accreased the apparent brightness of the red light, sa, cepted as finally settling the long dispute among for instance, a better burning, or even a quite rephysicians, as to the trustworthiness of Tyndall's cently lighted lamp, a red glass of less thickness or observations as to the effect of water vapor. slightly different tone, or of less absorbing power With an apparatus of the simplest character, in- than usual, these and many other possible vans volving no care and no expense, it was found that tions would lead him to mistake a red light for s water could be made to boil on the wintry peak of green one. In the same way, anything wh Whitney in the midst of the ice and snow, by the diminished the apparent brightness of a green light simple, direct action of the unconcentrated solar as a thicker or more absorbing glass, a badly burn rays. A newspaper statement, made before the ing lamps, the intervention of steam, smoke, expedition started, about the theory of the "blue fog, would render him liable to commit the cos sun," attributed to Prof. Langley, had a certain paratively harmless mistake of taking a grea foundation in fact, in articles which he has recently light for a red one. To the green-blind, on the communicated to the French Academy of Sciences other hand, the reverse conditions would obtam and elsewhere, to the effect that our own atmo- To him, the green light would be comparatively spheric action in modifying the solar heat and light dim, and the red one comparatively bright; so that to us, though of such enormous importance to all any of the conditions which would brighten the red forms of life on this earth, was, in reality, so little light and make it more conspicuous to the norma understood that it was now shown by him for the sighted, would render it more like green to the first time that owing to the selective absorption of green-blind, and would directly serve to temp the atmosphere our sun had never yet beenseen by him into danger. It has been well observed by Dr. anyone in its true colour, which would seem to us Joy Jeffries that no right minded and conscientions blue if the intervening atmospheres were removed. person would undertake the guidance of a train. 2 This actual blueness of the sun, a fact so contrary the announced condition that, in any variation: a full week's journey by waggon, and all arrange- to all recorded experience and so novel, was cited atmosphere and weather, he was to recognises dr ments had to be carefully made in advance. We less on account of its own practical importance light as a danger signal, and a bright light a finally left San Francisco, July 22, and went by than as an indication of the immense results caused safety signal, and vice versa, and that his own Lo the Southern Pacific Railroad to Caliente, about by this selective absorption, and one prominent and the lives of the passengers, were to be depred 300 miles from San Francisco. Some of the party object of the expedition was to determine by means ent upon his always rightly determining which disembarked here, from which point the stage line of the bolometer, an instrument recently invented starts across the desert to Lone Pine. Caliente is for this purpose by Professor Langley, the laws of a miserable little excuse for a town, comprised of this absorption and the resulting effect on climate. a hotel, a saloon, and one other house. The The instruments used for this purpose were many remainder of our party went on to Mogave, about of them invented for this special end, while others 50 miles farther, intending to cross the desert by were supplied by the kindness of eminent French waggon. The drive from Caliente to Lone Pine investigators, who interested themselves in the was anything but a pleasant one. The stage road results of the expedition. Summing up the results ruus through an arid alkali desert, with nothing generally, the only way in which they can be to see but sand, sage brush, and "side-winders," spoken of thus early, they are very satisfactory. as the natives call the horned rattlesnakes from their The report to the Government will tell the story nsinuating manners and treacherous disposition. of the work and its scientific results in detail. I will be remembered that early in July last, Prof. S. P. Langley, of the Allegheny Observatory, started for Mount Whitney, in California, in order to make observations of the sun, &c., from an altitude of between 14,000ft. and 15,000ft. above sea-level. The instrument used in measuring the solar heat is known as the bolometer, and was devised by Prof. Langley, its action being due to the lessening of the electrical conductivity of metal through a rise of temperature. The party comprised some officers of the Signal Service, a chemist, &c., and the following items, which we extract from an American paper, are ostensibly the results of an "interview" with the professor. Mount Whitney is believed to be the highest peak in North America; it is the highest in the Sierra Nevadas, and from the surrounding conditions was considered well adapted for the purpose in view. It is far removed from the borders of civilisation, and over a hundred miles of alkali desert lie between it and the nearest railroad, but the most authentic accounts of it described it as a place that should suit our purpose admirably. We had about 5,000 pounds of apparatus and 10,000 pounds of quartermaster's stores to transport Across an Alkali Desert, which. It has often been maintained that we hear y little of accidents actually arising from colu blindness; but it must be remembered that, a quite lately, this cause of neglect or mistake signals was scarcely recognised by those w duty it is to investigate such occurrences. A present day, the first inquiry which would be st in any case of over-running a danger would have reference to the colour vision of t The substance of a series of Canter Lectures detry col before the Society of Arts, |