last week, the president, Mr. Le Fevre, gave an account of the electrical stationary balloon, invented by M. Jules Godard and M. de Fonvielle. In the centre of the car, poised on a vertical axis, is a disc, which is in an electric circuit, and by some means, not clearly explained, keeps the car in equilibrium. The current, derived from a Faure battery, is also employed to work a small screw, so that the balloon can neither ascend nor descend. Mr. Le Fevre said the result would be that "the law of gravitation would be overcome, and that we should be able to suspend a body in the air at any altitude, and in any position.'

Mr. Edison has, it is said, offered to light some shops at the West-end, with incandescent lamps for six months free of all charge.

gradually habituated to it, by mixing the maize It gave an invisible spectrum 25 to 40 per cent.
at first with bran and oilcake. But in a few longer than the other.
days they will eat enormous quantities of maize
alone so long as it is green and tender. (They
are previously fed about three months with
clover alone.) Now, whenever the maize régime
is fairly started one notices three things: (1)
The quantity of milk diminishes: likewise (2)
the proportion of the cream to the milk; and
(3) less butter is obtained from the milk. The
butter, too, becomes white like that of winter.
These effects are more pronounced as time goes
on. They may be counteracted with a little
bran and oilcake. M. Genay finds it still advan-
tageous to sow a certain quantity of maize, be-
fodder may prove a valuable aid in the main-
cause in years with a very dry summer, this

tenance of the cows.

The difficulty in connecting light-ships with the shore, by means of telegraph cables, appears M. Decharme has begun the study of a new to lie in the fact that a suitable connection at the kind of figures produced thus: Red-lead, in fine ship-end is wanting. In storms these vessels powder, is diluted with water, and a horizontal pay out cable by an automatic arrangement-glass-plate is covered with a thin layer of the sometimes many fathoms-and an apparatus is mixture, on which drops of the same mixture wanted which will also pay out the electric cable. are then let fall. One thus gets pretty regular A statue is to be erected in Franche Comté to fine radii, and in concentric rings, the whole figures formed of red-lead arranged in extremely Claude de Jouffroy, who is said to have invented forming very varied designs, according to the steam-vessels about 1751. At Boulogne, a thickness of the layer or that of the drop restatue was inaugurated on Monday to Frederic ceived, and especially according to the length of Sauvage, the inventor of the screw propeller, fall. The figures have apparently some analogy which he exhibited in 1832. In 1835 our to those of circular plates, studied by M. Government offered Sauvage a sum of money on the condition that the invention should become the exclusive property of England; but although Sauvage was poor, he declined the offer. He died in the Picpus asylum at the age of 71, a pensioner of the State.

Decharme. One may obtain, according to experimental conditions, the three systems of acoustic figures observed by Chladni, diametral, circular, and compound figures. In M. Decharme's experiments these systems generally coexist; but one or other may be made to predominate at will. Prof. Cantoni has been appointed director of A correspondent of Les Mondes, M. Voitellier, the meteorological observatory, to be erected at describes a contrivance of his to prevent birds Pavia. Observations are to be made on the in-flying, without recourse being had to any mutifluences of light, heat, and electricity upon lation or cruel operation on the bird. It convegetable growth, in addition to the ordinary sists of a small (partly skin-covered) chain, one meteorological and magnetical work. end of which passes round the first feathers of the wing, while the other passes round the body of the wing, and is attached to a sort of swivel in the middle. The bird can move the wing freely, but cannot extend it sufficiently for flight. In position, the fetter is quite invisible, and the bird retains its elegance and ease of movement. M. Voitellier applies his system to peacocks, ducks and fowls; often, also, to birds of high value, but somewhat wild. He keeps num bers of pheasants and partridges in his garden, till he has occasion to let them loose, when they escape as readily as if they had been reared in the woods. Several gamekeepers have adopted his fetter. In the close season the pheasant breeders have been accustomed to collect all the birds required for reproduction, and to inclose them within netting till hatching was over; (inclosed in wire-work these wild birds sometimes kill themselves). But their wings must not be cut, for they have to be set at liberty in a few months. Accordingly the fetter has proved very acceptable, as extensive inclosures may be dispensed with.

Lissajous figures with sand, is described by Dr. A simple lecture method of producing the Weinberg in Carl's Repertorium. From the upper corners of a rectangular frame, two cords converge to a point, where they pass through a small piece of thin lead pipe, then down vertically to a little ball of lead hung to them. A piece of cork is adapted to the ball, so as to hold a test-tube filled with fine sand, and drawn out to a fine point with aperture below. A large sheet of paper is placed underneath. The ball being drawn obliquely out of the position of rest, and let go, and the finger that has been apformation of the Lissajous curves on the paper plied to the hole of the test-tube withdrawn, the

commences.

The pendulum can be shortened or lengthened by an arrangement on one side, which admits of the cord being pulled in or let out.

USEFUL AND SCIENTIFIC NOTES.

Machinery for Aerial Navigation.-Mon

the car

signor Capel and the Rev. A. de la Pauze obtained
provisional protection for an invention which is
thus described :-The object of our invention is to
provide an aerial locomotive which will be at once
economical in its working, speedy, buoyant, and
dirigible. Hitherto in most of the machinery or
apparatus employed for navigating the air too much
attention has been paid to buoyancy at the expense
of dirigibility, thus allowing the car and balloon to
be more or less, if not entirely, at the mercy of
currents of air. Our invention consists in a suitable
strength. We may construct it of bamboo, or of
car or boat built as lightly as is consistent with
the light weldless steel tubing now manufactured,
the whole being trussed or stayed together in the
strongest yet lightest manner.
The framing may
be covered with oiled silk or any suitable light air
and waterproof covering. In the centre of
we place a light strong mast
or pillar, on the top of which a large
light extended plane surface is balanced or
suspended, proportioned to the weight and force of
the car or boat, and preferably consisting of a light
framing over which a covering of oiled silk, light
varnished or coated canvas, or other suitable air-
proof material is rigidly stretched. This plane may
be inclined either upwards or downwards. Sup-
ports or stays extend from the mast or pillar to the
ends of the boat or car carrying bearings, and in
socket, or other form of universal joint, to which a
each bearing is mounted a Hooke's, ball-and-
fan or propeller is attached, so that the fans or
propellers driven by motive power propel the car
or vessel, and, receiving lateral motion from the
gearing, steer the vessel. The propellers may be
actuated by light steam, gas, or other explosive,
or by electric or other engines, or by air or
gases compressed into tanks at stations, and

these tanks

The idea of propulsion by means of the screw seems to have occurred to the fertile mind of Leonardo da Vinci towards the end of the fifteenth century. It is well known that he was all his life more or less occupied with the problem of flight, and in one of his works is a drawing (reproduced by M. Govi in a note in Comptes Rendus), which represents a large helix made, as the descriptive notes indicate, of iron wire with linen cloth having its pores stopped with starch, and connected by cords to a disc supporting the axis. This instrument (he says), if well made and whirled rapidly, would rise, screw-like, in the air. He seems to have made small paper models, the axis of which consisted of a thin slip of iron, which was twisted, and then left to itself, giving the necessary motorforce. M. Govi also furnishes proof that this carried by the car and their remarkable genius conceived the idea of the expansive contents used to actuate the engines. parachute. If a man had a tent of starched We mount the car on light wheels, which may be fixed on elliptical or other springs to ease the cloth (he says) 12 "braccia square and 12 bumping of the car on touching the ground. In high, he might throw himself from any height using the apparatus the plane surface above the without fear of danger. (A drawing is added.) car is fixed in a horizontal position, and the latter In the Norwegian division of the Paris Ex- The absorption of ultra-violet rays by certain being placed on a level road, the engines are hibition there is shown a woodpecker caught by media is being investigated by M. De Chardon-started and the car runs forward. The plane surits beak on the top of a telegraph-post. The net. One method adopted is to direct a beam When the desired elevation is reached, the plane face is then inclined upwards, which lifts the car. naïve account given informs you that this poor through a liquid in a trough with parallel glass surface is gently lowered to a horizontal or nearly bird became a victim of the sound produced by or quartz sides, to Poitevin's photochromic horizontal position, and the propellers still conthe telegraph wires, which it mistook for that of paper (which indicates, by change of tint, the tinuing to revolve, the car travels horizontally certain insects on which it feeds. According to presence of actinic rays). In a second method, forward. To descend, the plane-surface is inclined L'Electricité the sound of this vast Eolian harp, a solar beam from a heliostat is sent through in the downward direction. The descent is faciformed by telegraph lines, has produced other a slit, an objective of quartz and Ice- litated by steering the apparatus in a circular effects not less singular. Thus wolves have land spar, and a prism of the spar, to a direction. completely disappeared, because of it, from photographic plate or fluorescent screen; then districts where they were previously numerous. a trough half filled with liquid is put before the slit. The author finds that the liquid circulating The regular administration of salicylic acid to in plants, or impregnating roots and fruits have cattle as a preservative against spleen disease all an avidity for chemical rays. Fluorescence (called sang de rate), is known to have been prac- does not seem to be directly related to intensity tised some time by Herr Ludloff, a cattle-breeder, of actinic absorption; thus decoction of radish near Gotha, with the best results. It has been absorbs less than decoction of potatoes, yet the alleged that such treatment is prejudicial to former is without the property, while the latter reproduction. Herr Ludloff shows by statistics, is not. White wine is weakly fluorescent; red however, in a letter to Dr. Quesneville (Mon. Sci.) that, given in the small quantities he specifies, one gramme a-day per head of large cattle, it has no such effect. The experience ranges over four years and a half.

Feeding cows with green maize has been lately under consideration in France. In a note to the Journal d'Agriculture Pratique M. Genay gives his experience in this matter. With proper manuring he got as much as 155,000 kilogrammes of maize per hectare. He says the cows don't take to this fodder very well. They have to be

wine does not fluoresce. Of the few animal
liquids examined, blood is found a powerful
absorbent; but the aqueous humour of a calf's
eye, and the albumen of eggs, have no action on
chemical rays. Distilled water, alcohol, sul-
phuric ether, collodion, and solution of cane
sugar are also inactive. Gelatine intercepts all
the chemical rays, and it is sensibly fluorescent.
Comparing two simple photographic objectives,
of equal focus, one made by Darlot, of Paris,
the other by Dallmeyer, of London, the author
found the latter considerably more transparent.

AMONG the latest uses to which it is proposed to put the electric light is the illumination of rivers to permit the rafting of logs at night. The Muskegon Boom Company will be the pioneers in been made with a view of illuminating water at this direction. In Baltimore experiments have night to a depth of 200ft. Such a means of illumination, it is believed, would be of great service in searching for lost treasure and drowned persons, in raising wrecks, removing torpedoes, and other subaqueous labours.

AT the Royal Manchester and Liverpool Agricultural Society's Show, held at Blackburn on the 1st, 2nd, and 3rd inst., Messrs. W. H. Bailey and Co., of the Albion Works, Salford, Manchester, exhibited their slow-combustion hot-air engine, for its excellence and superiority. for which they obtained the first-class silver medal

ALTHOUGH theory would appear to indicate that in heating large rooms by steam-pipes, the pipes should be placed near the floor, it is now quite generally conceded by those who have tried both plans, that better results are obtained by locating them overhead.

"I would have everyone write what he knows, and as much as he knows, but no more; and that not in this only, but in all other subjects: For such a person may have some particular knowledge and experience of the nature of such a person or such a fountain, that as to other things, knows no more than what everybody does, and yet, to keep a clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original." -Montaigne's Essays.

SELENOGRAPHICAL.

[19186.]-THE Selenographical Journal, Aug. 24, 1881, contains a letter from Mr. Neison, in which are some important passages, which, for the benefit of those readers who may not have access to the journal, and who take an interest in lunar matters, I take the liberty to quote:

unless they are well acquainted with the forma- spoiling definition, and intend to order a țin.
tion which they have under examination. This periscopic right away.
is particularly the case with the formation Hip- About an inch of the edge is somewhat imper-
parchus adduced by Mr. Neison; a map of this fect; but for "clusters" and nebule, the whole
formation has been before the astronomical public aperture can be used.
during the last eleven years, and may still be had
of Mr. W. Wesley, 23, Essex-street, Strand; it
contains 115 distinct objects, 31 of which are
craters and craterlets laid down in their proper
positions, accompanied by a list in the order of their
magnitudes, and their measurements given in
seconds of arc. The letterpress also contains notes
of the most conspicuous objects, as well as a com-
parative description of two excellent photograms
by Rutherfurd and Gill.

My first speculum had a focal length of 61in., and I wished my new one to have about the same; but, on a cloudy day, I worked too long at the rough-grinding, and got a focal length of 57in. I then removed several of the central squares, and finished grinding with flour and washed emery. I now had a focal length of 60 in. At the end of figuring," the focal length was just 61in., or in. less than my first speculum, which, I think, is as near as an optician could come with grinding. tools.

46

Strong Probability of the Existence of an obscuring Medium in the Low-lying Districts of the Moon.Mr. Neison, in the last paragraph of his letter, has pine wood, the grain crossing, and glued and My polishers are constructed of two pieces of this remark:-"I think.... that it is not improb- screwed together. The smaller ones are made of able that there may be a real local haze or obscuring thin discs of plate-glass, and are 41, 21, and lin. medium at times overspread the interior of Plato in diameter respectively. The pitch covering them and other deep walled plains. There seems to me was of such consistency that a piece of the tem some weighty evidence in favour of these, and I perature of the room would receive three clear am aware of no sound objection, either astro-impressions of the "milling" on the edge of a 5nomical or chemical, against the possibility of this dollar gold piece, when the latter is allowed to occurring." In connection with this view, we find rest on the edge for sixty seconds. A light frame on p. 36 of Mr. Neison's book on the Moon the is made to hold the piece upright, without influenfollowing passage: "It appears probable that a cing its weight. very small residuum of aqueous vapour may, if not Lassell, and I can certify it has given good This is the rule given by Mr. must, exist upon the surface at times and in places: results. for owing to the tenacity with which such material as composes the surface retains moisture, it does not seem likely that by the influence of the surface already containing a certain amount of moisture the extreme outer layer that is most favourably placed for absorbing the aqueous vapour could be entirely denuded of it." If this be so, then a certain amount of moisture must be liberated when the temperature of the surface increases beyond a certain degree. As has been already observed, it is in the interior of the deep formations that the last here accordingly would the most favourable contraces of the lunar seas must have lingered, and dition exist for the liberation by the solar heat of a temporary vaporous covering.". In conclusion, I beg to recommend to the consideration of every student of the Moon's surface letter 19164 in the

Leytonstone, Sept. 12.

W. R. Birt.

GRINDING AND POLISHING A 9in.
SPECULUM-NEW METHOD OF TEST-

able trouble in getting enough light to test by. I In using the "Foucault test," I have considerhave a strong light, and a series of holes, 1-32nd to 1-200th of an inch; but cannot get sufficient light to test by when using a hole less than 1-60th of an inch. But I have found a new method of testing, which, I think, gives accurate results. Take a pinhole about 1-60th of an inch in diameter, and notice its appearance with a high-power eyepiece (240 I have generally used), then draw out the eyepiece just a little, and the image, of course, enlarges.

Importance of Regular and Continued Observations. "My own experience is in accord with Mr. Elger's view (Vol. IV., p. 52), that as a formation is gradually studied, and additional experience is gained of its variable appearance, not only do the principal features become much easier to recognise, but many additional features are gradually recognised, which at an earlier period have quite escaped notice. The drawings which are constantly sent me frequently illustrate this in a most remarkable manner, the earlier drawings showing too low, it will give a bright or dark spot reNow, if any portion of the mirror is too high or only the larger features, and these often incorrectly spectively on the enlarging disc of light, and will figured; but as additional experience is gained, not be diametrically opposite the defect in the mirror. only do the drawings become more accurate, but I have been enabled by this to detect defects that many additional details are observed and deli-issue dated Sept. 9, 1881. neated. This is one reason why so many disI could not see in using Foucault's; and, when in tinguished astronomers have found it difficult to doubt with the latter as to the species of a defect, reconcile their own observations of lunar objects have resorted to the eyepiece test, and can judge of with those of more practised observers of the Moon, the nature of the irregularity in five seconds. I for however great may be their experience in was more troubled with rings and zones than irregularities, and now have a surface that Fouobserving with the telescope-experience gained ING AND SILVERING SPECULA. perhaps in double-star observations or in examincault's test does not show to have any irregulariing faint planetary detail-it will not compensate [19187.]-I was pleased to notice, in your issue ties, but this test reveals a few. Will" A. J. S.," for their inexperience in observing lunar details. of July 8th, an article by E. P. Aintree on the Mr. Bell, Mr. Blacklock, and other amateurs please Thus, when they attempt to examine any portion time necessary in grinding and polishing a specu-give their ideas in regard to this mode of testing, of the lunar surface, they find the greatest diffi- lum with a machine. Now, with your permission, whether it fails under any circumstances, and why? culty in detecting the smaller formations, and con- I will relate what I have done "by hand." My lamp is about ten-candle power, and has a sider as delicate objects readily overlooked-I have a Newtonian reflector-my own con- tin chimney, 14in. high; the pinholes are punched objects which more practised eyes would recognise struction 9in. aperture, and 61in. focal in a piece of tinfoil, and fastened in front of light. at a glance, and truly describe as conspicuous fea- length, which I ground by hand, following the I use a razor-blade for cutting off the rays at tures. The observations of Linné, made some "two discs" method described on page 593 of focus. During three years past I have used a fifteen years ago, afford more than one illustration Vol. XXVII. Although the short focal length, dozen or more receipts for silvering, and have alof this fact. So does the case of Hyginus N., which compared with aperture, makes the curve of ways been-until lately-quite unsuccessful; but, has been described as being a faint, inconspicuous speculum necessarily quite deep in the centre; yet, since using the formula described by Mr. Brashear object, difficult to detect, by both Otto Struve notwithstanding the greater quantity of material in volume XXXI., page 327, I have had success and Winnecke, and this on occasions when more to be ground away, I finished the rough-grinding every time. Have just silvered two 9in. specula, experienced observers have seen this curious for- in much less time than would have been necessary and a "flat," with perfect success. My method of mation with the greatest ease and distinctness. On had I used a machine. Thinking my speculum silvering, however, is different from any I have one occasion a very distinguished astronomer sent was not as perfect as I was capable of producing, seen described. I clean my mirror well, and place me a drawing of a portion of the Moon, which he I recently cracked" another disc from a large it face upwards, and pour on the solutions as declared did not agree in the least with my de- piece of thick glass I had, and began operations. deep as possible without overflow. The mirror is, scription of it, there being five craters, not four, I will first describe the "cracking process, as I previously, slightly warmed, and the solutions as I had stated, and I had given the relative sizes have never seen anything of the kind described in made of about twice the usual strength. In my all wrong. The real truth being he had mistaken your columns. I took the large piece of glass-case, the silvering is usually completed in from five considerable walled valleys, each twenty to lin. thick-and cut a deep circle with a dia- five to seven minutes. The mirror is then thothirty miles in diameter, for the four small craters, mond" on each side, and of the same size as the roughly washed and dried, and has a surface of no scarcely a tenth as large, to which my description intended disc. Then I heated an arc of this circle reflecting power whatever. I then go over it with a applied; and he had not even detected the four several inches in length, quite hot, over an alcohol camel's hair brush, and clean off the brownish pow small craters lying in their midst. Another such lamp, and then applied a piece of ice to the heated der which adheres, andthen polish for five minutes astronomer sent me a drawing of Hipparchus, in portion. The result was several cracks, running with a soft piece of chamois skin, the result being which he describes the three craters, Halley, Hind, in the direction of the heating portion. Selecting an excellent reflecting surface. and Horrocks, as small craterlets; and C, L, G, the one nearest the edge of the disc, I applied a and E, as extremely minute craterlets; not one of heated iron-white-hot-along the direction I the other craters was seen." wished the crack to follow, the result, of course, I have given the first paragraph of Mr. Neison's being a slight extension of the crack. letter in extenso, because it appears of great implying ice or cold water, the crack extends a little portance to attempt to reduce the observation of lunar objects to a system, for it is only by careful and continuous observations that the details of any particular lunar region can become well known, so that delicate and minute details, probably of an abnormal character, may be recognised, and as these are properly studied and pieced together in the delineation or description of the particular region under examination, those features that are constant may be separated from those that are occasional, the constant appertaining to, and are essential features of, the formation; the occasional being dependent on the interposition of a temporary vaporous covering. Hitherto, observations of the lunar surface have been conducted in a great measure, and with very few exceptions, indeed, in a very desultory manner, and the remarks of Mr. Neison are well calcula ed to show how easily even experienced and distinguished astronomers may misapprehend the true bearing of what they see,

"

Then ap

farther. In this manner I produced a very fair
disc, which I rounded in the usual manner, using
very coarse-grain emery.

The time occupied in the different stages was as fol-
lows:-" Cracking" disc, 1h. 30m.; edging disc, 4h.
30m.; excavating concavity, 6h.; covering grinder
with small squares of plate-glass, 2h.; flour-emery
and lengthening focus a few inches, 3h. and 5m.;
one-minute emery, 1h. 35m.; three-minute emery,
2h. 5m.; ten-minute emery, 2h. 5m.; constructing
four polishers of different sizes, 6h. 40m.; polishing
with large polisher, 90m.; figuring, 10h.; time
consumed in testing, about 5h. Total, 46h., which
is less than half the time it took Mr. Aintree with
a machine. I won't say I have as perfect a figure
to my mirror as he has; but it is perfect enough
to more than pay me for my trouble. The highest
power I have is a lin. periscopic eyepiece, giving
a power of 122, and there is no falling off in deti.
nition. I think I can double the power without

I was guided to this method of silvering by noticing that the glass silvering-vessel used always received as heavy a deposit as the mirror, and the process is much more economical of distilled water, and that is quite an item with me, for it only takes about 4oz. of solution to silver a 9i8. surface, instead of a pint or more in usual process. I was for a long time deterred from making a speculum, on account of not wishing to make a machine; but was glad to learn a machine was un necessary, and I would advise the amateur every time to grind and polish by hand, unless he cau have the use of a machine without taking the trouble to make one. If the Editor wishes, I will describe in my next an admirable substitute for an observatory, which I constructed in about a day and a half, at a in money of only idols. 30cents (about 188.; probably, in Eugland, the cost would not exceed 8s. or 10s.), and which answers perfectly the purpose for which it was intended. Harry L. Baldwin, jun. 231, Kansas-avenue, Denver, Colorado. August 22. [Please send.-ED.]

cost

GRINDING EDGES OF GLASS SPECULA. [19188.]-I BEG to tender my experience with regard to the edges of glass specula. I once attempted to grind and polish a speculum with the edge rough, and can assure our readers the job was one of great difficulty. It required most careful washings between the different grades of emery used, and even then a grain or two would sometimes remain concealed in some crevice (in spite of careful brushings in water), find its way to the front, and cause scratches; small bits of glass would chip off from the edge, causing great annoyance, although this evil may be avoided by grinding a bevel first. I do not say it is impossible to finish a speculum with the edge rough, but I do say it is most unadvisable, slovenly, and unworkmanlike. Having decided that the edge should be ground, I proceeded somewhat like others have who since then have described their methods in these pages-viz., in a lathe, using a piece of zinc and coarse emery. This succeeded very well, and I was quite satisfied with the result; but it took several hours (I do not recollect how many), and was a most tedious and monotonous job. I'next ordered a disc with the edge ground, determined to have nothing more to do with grinding edges; but by some mistake it arrived in the rough. Of course I was a little disappointed, but set to work on the edge with a diamond tool I procured for the purpose, and in about two or three hours got it into shape. I then finished the edge with fine emery and a strip of thin brass. In conclusion, allow me to say: firstly, be sure to have a nice ground edge; secondly, if possible, get it done for you; thirdly, if you do it yourself, the diamond tool is the quickest.

ECLIPSES.

A. N. H.

[19189.]-IF "F.R.A.S." will be kind enough to re-read my question, he will perhaps find that it deserves a somewhat more courteous answer than he has given. The solar eclipse limits are about 13 and 183, which means that if at conjunction the Sun is less than 131 from the nearest lunar node a solar eclipse is certain at that conjunction; if more than 18 there is certainly none; if between 13 and 18 an eclipse is doubtful, and more precise calculation of the actual facts required to remove the doubt. From these data, and the further data of Sun's average daily motion (59' 8-33"), and average daily regression of lunar node (3′ 10.6"), it is easily seen that there may be two solar eclipses every time the sun crosses a lunar node, one at the conjunction preceding the node, one at the following conjunction. My difficulty is to prove that there must be one solar eclipse at every passage through a node (before or after); or again, that there must be two in a year.

L.

me that I recently saw at the Paris Electrical attaching of a lamp to a micrometer in such a way
motor which, whilst efficiently as to readily show the wires. In the course of
Exhibition, a
answering the purpose, was very much smaller and attempts to improve the illumination of one micro-
less clumsy than the one above alluded to. It was meter in particular, on the 6in. equatorial, which
shown there as applied to the working of a lock- had all the defects of all micrometers and none
stitch sewing-machine. I am unable accurately of their excellences, various results were obtained,
time as being the simplest and best as well as the cessful; but when the micrometer was attached to
to describe it from memory, but it struck me at the which, so far as one could see, promised to be suc-
smallest thing of the kind I had seen. Externally the telescope, and moderately close and unequal
it was elliptical in shape, apparently measuring double stars sought to be measured, the light was
about 7in. by 4in., and was fitted upon the axle, found to be an utter failure for any such work. It
which usually carries the driving-wheel of the is hardly necessary to say that almost any plan
machine; the axle was extended through the will answer fairly for measuring wide and bright
standard, and terminated just outside it by a small stars; but the time has gone by when it is worth
grooved wheel, over which a round band was passed while giving a fine telescope to such work any con-
and connected to the machine on the table above siderable part of the time.
in the usual way. When put in action the motor
was caused to revolve with great rapidity, carrying
the axle with it, the speed being reduced to the
required rate by the proportionate sizes of the
grooved wheels. The motive power was derived
from a form of bichromate trough battery of five
or six cells placed on the floor within easy reach of
the worker, and the machine was started or stopped
by a simple contrivance for immersing or with-
drawing the plates from the fluid.
weighed considerably less than the fly-wheel and
treadles which it superseded, and its efficiency was
demonstrated by the young lady in charge who
worked with the machine at frequent intervals.
The motor is exhibited by "The Electro Dynamic
Company," 2009, Pine-street, Philadelphia, and
may be seen in the nave on the ground-floor,
American Section, class 9, No. 1141; the battery
employed being No. 1097, class 2, by the same
exhibitors, from whom (or from their representa-
tive, Mr. Griscom) it would no doubt be easy to
obtain further particulars.

The motor

R. T. Lewis.

HEATING-SURFACE OF MODEL

BOILERS.

The accompanying engravings, from photographs of the micrometer and the lamp attachment, will make plain the end-illuminating plan used at this observatory. The square micrometer box in front of the position-circle is exactly 6in. in length, and from this the dimensions of the various parts will be easily seen. A is the lamp, moving freely around the horizontal end of the tube C, and kept in a vertical position by the weight E. The light from the lamp passes into C. and after a reflection from a mirror in the angle of C, passes through H into the micrometer-box, and directly on the wires. The rod F is screwed firmly into C, and forms an axis about which the latter turns freely. The counterpoise D attached to C by a bent arm, keeps the shorter arm of C, to which the lamp is attached, always horizontal. The long arm I is sufficiently bent or curved to allow the lamp to swing through it in any portion. I is attached by a set screw, N, to the plate in which the micrometer-box slides when the bisecting screw K is turned, so that the additional weight of the illuminating apparatus has no connection with the bisecting and micrometer screws. The tube C fits loosely over H, forming a support or bearing when the longer arm of C is in a hori[19192.]-Ox page 504, Vol. XXXII., "Sunlight" gives as his rule "15 square inches of heat-zontal or inclined position. H passes inside C ing surface for every circular inch of diameter and perhaps half an inch in the normal position of the box. This distance is increased or diminished as stroke." As an example he gives 12in. by 4in. 48 square inches, as ample surface for a pair of the lamp A is made of tin, open at the bottom and the bisecting screw K L is turned. The outside of cylinders 1in. by 14in. If I understand the wording of his rule, it may be formulated thus inside diameter of A, so as to give a free draught, top. The lamp itself, somewhat smaller than the S = 15 (D2 + L) where S = heating surface in square inches; D is inserted from the bottom, and held in place by diameter of piston in inches, thin brass springs attached to the lamp and presslength of stroke in inches. If that is 80, ing against the inside of A. For some weeks past, surely the two cylinders (cutting off at half-stroke) gas has been used in place of the lamp, a small flexwould require 15 (1·5 × 1·5 + ·75) x 2 = 90 square ible rubber tube being attached to B, and running inches of heating surface, whereas he gives only up the telescope tube over the intersection of the 48 to 54 square inches. If I misunderstand his axles, and thence down the pier to the floor. This rule, will be kindly set me right? In applying rubber tube is always in place, not being disturbed this rule to tubular boilers, does he reckon the by reversing or moving the telescope in any posiefficiency of heating surface in tubes according to tion, and is more convenient than an oil-lamp, Molesworth, or is it near enough in model-work to which requires more or less attention. It will be reckon tubes as equal in efficiency to flat horizontal readily seen that the micrometer lamp will always maintain a vertical position, no matter what the position angle of the wires may be, or the place of the eye-end of the telescope. The light from the lamp is coloured or diminished at pleasure by means of the slot in A, as shown. The edge of the lower part of the arm I, for convenience in counterpoising, fits into a slot in one of the diagonal hol

and L

=

surfaces?

=

Glatton.

THE POSITION MICROMETER OF THE

WASHBURN OBSERVATORY.

[19193.]-THE micrometer attached to the 15in. equatorial of the Washburn Observatory was furnished by the makers of the telescope, Alvan Clark

and Sons.

micrometer, and a new method of illuminating the
A good many changes have been made in the
wires devised, which in practice has been found
very satisfactory. It has been fully tested by
making several hundred double-star measures,
and such changes and further improvements made

as were deemed desirable.

LIGHT-DRAUGHT STEAMERS. [19190.]-I FEAR that what Mr. S. E. Peal (letter 19158, p. 623) asks for is an impossibility. The displacement of a craft 80ft, long, 20ft. wide, and lft. draught of water may be taken at 36 tons. Now, the weight of this boat we may call 16 tons, leaving only 20 tons carrying capacity if fitted as a barge, without engines. The engine and boiler being 83 tons, and coal estimated at 1 ton for every 60 miles it would be necessary to travel without coaling, leaves only about 8 tons, I suppose, carrying-capacity at that draught. If there is water enough, however, she might be loaded to 2ft., and she would then carry 46 tons; lin. of immersion may be roughly reckoned at 3 tons displacement. At the first glance, I was inclined to propose a boat 15ft. wide, with four narrow side- class requiring the most perfect illumination of the wheels, as I thought the great weight of machinery wires possible, being for the most part very close pairs The double stars regularly measured are of the at one end to drive stern-wheels would depress the stern too much, but I find, on making some calcuor very faint companions and unequal pairs. In many lations, that when unloaded the stern draught cases it would be simply impossible to use a bright field and get satisfactory results. My experience is would be only 12 in., the mean draught being Stin. that the bright wire illumination is practically much To obtain sufficient strength to withstand the the best for all purposes, and beyond all doubt the strains of weight at the extremities, recourse must be had to some unusual means, and I think bow-best for the most important double-star work. All string girders best. They should be three in number, one amidships and one at each side, rising to about 6ft., and stayed at intervals of 10ft. Two paddle-wheels, 8ft. diamater, floats 4ft. 9in. by The engine had better have a single cylinder; it will scarcely be necessary to work the paddles independently. Diameter of eylinder, 15in., stroke 30in. It would be well to have a small condenser to supply clean feed-water if the rivers in Asam are as muddy as the Hooghly. Such a boat would have a speed of about 8 miles per hour, and would consume about 1 ton of coal in 7 hours. It would be well if the length could be greater; with the restrictions in size and draught, all I can lead Mr. Peal to expect is: Carrying capacity 10 tons, with coal for 100 miles steaming. Sept. 8th.

20in.

SMALL ELECTRIC MOTOR. [19191.]-ON reading the description given in the last number of "Ours" (19182, p. 16), it occurs to

my attempts to use a bright field have been wholly
disappointing. The great trouble heretofore in using
bright wires has been to avoid stray light in the
field from the micrometer lamp and get sharp and
uniformly bright wires in the varying positions
they must take. In the Fraunhofer diagonal-arm
plan generally used, it is necessary to rotate the lamp
with every change of the wires in position angle, so
through the micrometer-screw and the axis of the
as to bring the lamp into the plane which passes
telescope-otherwise the light is feeble, and the
wires, when brought within two or three diameters
shadow is cast on the wire or the light more or less
of the webs, are indistinct and hazy. Again, a
reduced when the lamp is placed in the proper po-
sition with reference to the wires, by the partitions
between the holes in the tube of the telescope
through which the light passes from the hollow
arms. Many other devices have been suggested
and used; but it is questionable if any plan has
been thoroughly tested in actual practice better
than the one last referred to, notwithstanding its
many defects. Indeed, nothing is easier than the

low arms, and turns the latter with it. To the shown in the engraving) sufficient to balance the opposite hollow arm a weight is attached (not micrometer lamp and its attachments. The lamp, tubes, arm, &c., should be made as light as possible; but I should be rigid enough to have noappreciable flexure in the different positions. In the micrometer described, the entire weight ofthedevice perhaps more. The effect of the light on the wires is the side of the wires opposite H a slip of glass or is 260z; this could be probably reduced 60z., and greatly improved by putting within the box and on other reflecting material, in such a position that the wires can be seen reflected in it looking into the

tube C. The light is thereby reflected back on the wires, illuminating them on both sides, and making them as near as may be symmetrical.

It is

Other changes have been made in some of the working parts of the micrometer, which have been shown by experience to be of very great importance. on the side opposite the nut and fitted with an The bisecting-screw K has been extended additional head, L. The pinion for rotating the micrometer-box has been changed to a point opposite K, and is moved by the milled head M. either K and M or L and M must be used simulhardly necessary to say that, in measuring angles, taneously, one with each hand. If the micrometerscrew is anywhere near a horizontal position, K with the right. If the micrometer-screw is more will naturally be used with the left hand, and M nearly vertical, L and M will be used. In the same way, in measuring distances, K and P or L and P will be used at the same time-the former when the box is horizontal, and the latter when it is more nearly vertical with respect to the observer There is no position where it is not entirely convenient to use one or the other in all measurements-an important advantage, not found, so far as I know, in any other micrometer.

the observations well. Mr. Westlake's statement that "to divide this clearly with 250 is good work for any mirror" is absurd. The little star at about 300° 20' is of a beautiful indigo-blue hue in my 6in. Calver. Mr. Common has found three much fainter companions with his 18in. reflector. The pair alluded to by Mr. Denning (letter 19112) is 383. E gave 80, 90: 120-122: 5.687": 1830. There has been no change since. Sept. 6.

if the eyetube were out of adjustment, and the flat and mirror set at night on a star concentrically, though without knowing it, say, at a focus of 200, and then examined by day, with the tube farther out, say, focus of Kellner, when it would be eccentric.

Neither of these are, however, satisfactory explanations, particularly to Mr. Calver.

In investigating the relations of the mirror, flat, eyetube, &c., and their connection with the cone of rays, I came upon a curious fact, which is no doubt well-known to opticians-that the axis of the cone of rays from the mirror does not fall upon the centre of the flat-that is, on its minor axis; and I shall be glad to place this before your optician readers and correspondents, and invite their opinions as to whether any allowance has to be made for this, and what effect it has, or if any, on the adjustment of the flat and mirror.

This is readily seen in the following figure. A B represents the flat, full size, showing section of cone 2in. diameter at the point where it meets the flat at C, 9in. distant from the focus. EE is the axis of the cone, and F FF F the sides of the cone. The flat makes the angle 45° with the axis, which I find is also the correct re-entrant of the sides of the cone. This is easily ascertained as follows:Set the flat A B at 45° with the axis, and draw a line from the focus, 9in. from C, through the point D, lin. from the flat at C, and continue it till it reaches the flat at A. From A draw the line A F, one of the sides of the cone towards the mirror making the angles a and a equal to one another. Draw the line A G from the point A parallel to the axis, and mark off AE equal to EF. Make the two angles b and b equal to one another, and draw the line FB at that angle till it meets the flat at B. Make the angles c and c equal to one another, and draw the line BF at that angle, which being extended will meet the starting-point at the focus of the cone.

It will now be seen that the part of the flat BC is shorter than CA, and the difference appears to increase with the increased size of the flat, in proportion to its distance from the focus. Without any further comment, I leave this with your correspondents. Does this in any way affect the adjustment of the flat and mirror? Fordingbridge.

T. Westlake.

THE AUBURNDALE METALLIC THERMOMETER. [19196.]-HAVING lately examined the works of this new machine, I take pleasure in forwarding a sketch. A, B, the compound laminæ, fixed at G,

particular explanation, only that the pulley on attachment makes no difference, and no more spindle is taken off A A, and placed on C the other trouble in filling the boiler. The stopper is taken way up, or small speed downwards, and the guide-out, the spring turned back on its joint, and the pulley E is reversed with bosses outwards. For contents of measure poured in through a funnel; fly-cutting the pillar which carries guide-pulleys, then the spring and stopper are replaced. Now, I

TLIT

slides on shank A, which puts the required tension
on the driving-gut, and secured with two screws
on the pillar B into slot in shank A. The shank
A passes through the tool-dome, and is quite
secure, is made of iron, and case-hardened;
the pillar is of iron, the spindle of cast-steel, and
the pulleys and remainder of gunmetal.
D. Young.

A SAFETY BLOWPIPE SPIRIT-LAMP.
(19198.]-EVER since I purchased a French blow-
pipe spirit-lamp some few years ago, the thought
has occurred to me as often as I had occasion to
use it, that the article, useful as it is, could never
be reckoned perfect without some means of knowing
when the boiler required replenishing, as if left to
get nearly empty, an explosion might occur. Hav-
ing often considered this desideratum in vain, the
thought recently occurred to me that the boiler
might be made to record its diminished contents by
its own diminution of weight. Being fully satisfied

BB

feed-pipe to pass through. In making this contrivance it is essential that the boiler should rest on its seat without in any way hitching-that is, it must be perfectly free to rise by the sole action of the new safety-spring.

Of course, this idea could be modified in many ways. For instance, a bridge might be placed over the boiler, and this have a short helical spring graduated to the required strength fixed midway under it, to which the boiler might be attached. F. M. Crichton.

A FAULT IN DESIGN OF TRICYCLES-
EQUILIBRIUM OF BICYCLIST.
[19199.]-I HAVE noticed a fault in the design of
some tricycles I have seen about, and, I believe, in
some of the newest patterns it is more noticeable

FIC./

FIG. 2.

but free to move the other end. F, F, "adjusting- of the feasibility of this plan, I have succeeded in
pieces" of spring-steel, screwed to A, B, and
et" by set-screw Z, Z.

P, a pin fastened to end of F, and working in slot of sector-piece D, so that as the lamina change their shape, the sector-pieces rotate around the x's H, which is placed at the centre of curvature of the sector; E, E, support the axis H, H.

carrying it out as follows:

In these. French lamps the boiler rests upon the top of the stove, and is pressed upon by a short bit of spring just behind the handle, to keep it tight and prevent its falling off. The handle is made removable by having a short steel blade at its upper end, which runs into a flat hollow socket fastened C is centre pinion, gearing into sectors; on axis to the upper part of stove. Removing this socket of C is indicating-needle, shown in dotted line. and the bit of binding-spring, which last must be Pinion C slips endwise out of gear to adjust the in-entirely discarded, I made a new socket of brass strument by aid of F, F. The machines are made with dials from 14in. to 12in. or more across.

"Roi ne puis, Souza je suis."

MILLING MACHINE. [19197.]-I HAVE at last sent you drawing of my milling machine, which I find an invaluable tool, and which, I hope, may benefit your readers. It will be seen by the drawing at once, without any

(B), and jointed to the back of it a piece of French
timepiece mainspring (A), shaped as in sketch, the
end of it having a circular hole to just admit the
feeding-pipe of the boiler passing through it; and
the stopper, with its safety-valve (D) being screwed
down over it, keeps it from rising up. This spring
is so graduated in strength as to be kept down by
the weight of the boiler when filled with the fluid
contents of the brass measure supplied with these
lamps, which is just two fluid ounces. This new