to it. Break up a piece of flint glass into fragments, about the size of the seeds of mustard, or a little larger-place one of these pieces on the ring of wire, and hold it in the point of the flame of a candle, or gas-light, when the glass will melt, and assume a complete lens-like, or globular, form-let it cool gradually, and keep it for mounting: others may be made immediately in the same manner, and if the operation be carefully conducted not one in twenty lenses will be imperfect. It may be remarked, that the smaller the drop the more globular it will remain, and consequently the higher will be the power of its magnifying properties. These lenses are not to be despised because of simple construction -on the contrary, few equal them in discerning power, the most delicate test objects may generally be very clearly discerned with much more distinctness indeed then by the commoner kinds of microsscopes, as sold at the opticians. Their magnifying power, too, is very considerable, varying from 30 to 200 times linear measure, or, as these things are popularly understood, they will magnify objects from 900 to 40,000 times.

The easiest methods of mounting, or fitting-up for use, minute lenses, is to put one between two pieces of brass, having coresponding holes cut in them of such a size as to hold the edge of the lens, or they may be fixed to a single bit of brass by a little gum.

Water Lenses.-Make a hole, about the size for a large pin to pass through, in a piece of thin brass -take up a minute drop of water with a pin's point, and place it on the hole, when it will assume a globular form, and be capable of showing with considerable distinctness microscopic objects placed beneath. This, besides being of such a temporary character, is subject to irregularities arising from the difficulty of holding it with the requisite steadiness, — the trembling occasioned by the breath, or accident,— by draughts of wind,-want of perfect sphericity of the hole, &c.

Varnish Lenses.-Sir D. Brewster long ago constructed fluid lenses in a different and superior manner. He placed minute drops of very pure turpentine varnish, and other viscid fluids, on plates of thin and parallel glass. By this means he formed plano-convex lenses of any focal length; and, by dropping the varnish on both sides, he formed double-convex lenses, with their convexities, in any required proportions. By freeing the glass carefully from all grease, with a solution of soda, the margin of the lenses was beautifully circular, and the only effect of gravity, which diminished with the viscidity of the fluid, and with the smallness of the drop, is to elongate the lower lens, and flatten the upper one. These lenses were found to answer well as the object glasses of compound microscopes.

Natural Lenses.-The crystalline lenses of minnows and small fishes may be taken out of the eye in a state of such perfection, that, when used as single microscopes, they give a very perfect image of minute objects. In such lenses, which have an increased density towards their centre, the spherical aberration is almost wholly corrected. Great care, however, must be taken to make the axis of the lens the axis of vision, to prevent its form from being injured by pressure against the aperture which holds it. The best way is to make a ring at the end of a piece of wire, having its diameter a little greater than that of the lens. A ring of viscid fluid, (gum water

for example,) is then made to line the ring of wire and the lens is suspended in the ring of fluid, some of the fluid encroaching upon its anterior or posterior surface.

COLORED CLOUDS.

THE rays from the rising and setting sun are refracted by our spherical atmosphere; hence the most refrangible rays, as the violet, indigo, and blue, are reflected in greater quantities from the morning and evening skies; and the least refrangible ones, as red and orange, are last seen about the setting sun. Hence Mr. Beguelin observed, that the shadow of his finger on his pocket book was much bluer in the morning and evening, when the shadow was about eight times as long as the body from which it was projected. Mr. Melville observes, that the blue rays being more refrangible are bent down in the evenings by our atmosphere, while the red and orange, being less refrangible, continue to pass on, and tinge the morning and evening clouds with their colors.-See Priestley's History of Light and Colors, p. 440.

But as the particles of air, like those of water, are themselves blue, a blue shadow may be seen at all times of the day, though much more beautifully in the mornings and evenings, or by means of a candle in the middle of the day. For if a shadow on a piece of white paper is produced by placing your finger between the paper and a candle in the day-light, the shadow will appear very blue; the yellow light of the candle upon the other parts of the paper apparently deepens the blue by its contrast, these colors being opposite to each other.

There is a bright spot seen on the corner of the eye, when we face a window, which is much attended to by portrait painters; this is the light reflected from the spherical surface of the polished cornea, and brought to a focus; if the observer is placed in this focus, he sees the image of the window; if he is placed before or behind the focus, he only sees a luminous spot, which is more luminous and of less extent, the nearer he approches to the focus. The luminous appearance of the eyes of animals in the dusky corners of a room, or in holes in the earth, may arise in some instances from the same principle; viz. the reflection of the light from the spherical cornea; which will be colored red or blue, in some degree, by the morning, evening, or meridian light, or by the objects from which that light is previously reflected. In the cavern at Colebrook Dale, where the mineral tar exudes, the eyes of the horse, which was drawing a cart from within towards the mouth of it appeared like two balls of phosphorus, when he was above 100 feet off, and for a long time before any other part of the animal was visible. this case the luminous appearance is supposed to have been owing to the light, which had entered the eye, being reflected from the back surface of the vitreous humour, and thence emerging again in parallel rays from the animal's eye, as it does from the back surface of the drops of the rainbow, and from the water-drops which lie, perhaps without contact, on cabbage-leaves, and have the brilliancy of quicksilver. This accounts for this luminous appearance being best seen in those animals which have large apertures in their iris, as in cats and horses, and is the only part visible in obscure places, because this is a better reflecting surface than any other part of the animal. If any of these energent rays from the animal's eye can be supposed to have been reflected from the choroid coat through the

In

semitransparent retina, this would account for the colored glare of the eyes of dogs or cats, and rabbits, in dark corners.

TEMPERATURE.

A DEFINITE degree of sensible heat, as measured by the thermometer. Thus we say a high temperature, and a low temperature, to denote a manifest intensity of heat or cold. According to Biot, temperatures are at the different energies of caloric in different circumstances. Different parts of the earth's surface are exposed, as is well known, to different degrees of heat, depending upon the latitude and local circumstances. In Egypt it never freezes, and in some parts of Siberia it never thaws. In the former country, the average state of the thermometer is about 72°.

The annual variation of heat is inconsiderable between the tropics, and becomes greater and greater as we approach the poles. This arises from the combination of two causes, namely, the greater or less directness of the sun's rays, and the duration of their action, or the length of time from sunrise to sunset. These two causes act together in the same place: that is, the rays of the sun are most direct when the days are longest, or at the solstice. But while, (the season being the same,) the rays become more and more oblique, and consequently more feeble as we increase our latitude, the days become longer, and the latter very nearly makes up for the deficiency of the former, so that the greatest heat in all latitudes is nearly the same. On the other hand, the two causes of cold conspire. At the same time that the rays of the sun fall more obliquely, as we increase our latitude, the days become shorter and shorter at the cold season; and according the different parallels are exposed to very unequal degrees of cold: while tropical regions exhibit a variation of only a few degrees, the highest habitable latitudes undergo a change amounting to 140°. Both heat and cold continue to increase long after the causes producing them have passed their maximum state. Thus the greatest cold is ordinarily about the last of January, and the greatest heat about the last of July. The sun is generally considered the only original source of heat. Its rays are sent to the earth just as the rays of a common fire are thrown upon a body placed before it; and, after being heated to a certain extent, the quantity lost by radiation equals the quantity received, and the mean temperature remains the same, subject only to certain fluctuations depending upon the season and other temporary and local causes. According to this view of the subject, the heat that belongs to the interior of the earth has found its way there from the surface, and is derived from the same general source, the sun; and in support of this position is urged the well-known fact, that, below eighty or one hundred feet, the constant temperature, with only a few exceptions, is found to be the mean of that at the surface in all parts of the earth. But how are we to explain the remarkable cases in which the heat has been found to increase, instead of decreasing, as we descend? We are told that in the instance of mines, so often quoted to prove an independent central fire, the extraordinary heat, apparently increasing as we descend, may be satisfactorily accounted for in a simpler way :-1. It may be partly received from the persons employed in working the mines. 2. The lights that are required in these

dark regions afford another source of heat. 3. But the chief cause is supposed to be the condensation of the air, which is well known to produce a high degree of heat. The condensation, moreover, becoming greater and greater according to the depth, the heat ought, on this account, to increase as we descend; and as a constant supply of fresh air from above is required to maintain the lights, as well as for the purposes of respiration, at the rate of about a gallon a minute for each commonsized light and each workman, it is not surprising, that the temperature of deep mines should be found to exceed that of the surface in the same latitude. This explanation of the phenomenon seems to derive confirmation from the circumstance that the high temperature observed is said to belong only to those mines that are actually worked, and that it ceases when they are abandoned. If we except these cases, and that of volcanoes and hot springs, the temperature of the interior of the earth seems to be the mean of that at the surface; and hence it is inferred that it is derived from the same source. The diurnal variation of heat, so considerable at the surface, is not to be perceived at the depth of a few feet, although here there is a gradual change that becomes sensible at intervals of a month. At the depth of thirty or forty feet, the fluctuation is still less, and takes place more slowly. Yet at this distance from the surface there is a small annual variation; and the time of midsummer, or greatest heat, is ordinarily about the last of October, and that of midwinter, or greatest cold, is about the last of April. These times, however, are liable to vary a month or more, according as the power of the earth to conduct heat is increased by unusual moisture or diminished by dryness. But at the depth of eighty or a hundred feet, the most sensible thermometer will hardly exhibit any change throughout the year. So, on the other hand, if we ascend above the earth's surface, we approach more and more to a region of uniform temperature, but of a temperature much below the former. The tops of very high mountains are well known to be covered with perpetual snow, even in the tropical climates. The same, or rather a still greater degree of cold, is found to prevail at the same height, when we make the ascent by means of a balloon. The tops of high mountains are cold, therefore, because they are in a cold region, and consequently swept by currents of cold air. But what makes the air cold at this height? It is comparatively cold, partly because it is removed far from the surface of the earth, where the heat is developed, but principally because it is rarefied, and the heat it contains is diffused over a larger space. Take a portion of air near the surface of the earth, and at the temperature of 79° of Fahrenheit, for instance, and remove it to the height of about three and a half miles, and it will expand, on account of the diminished pressure, to double the bulk, and the temperature will be reduced about 50°. It will accordingly be below the freezing point of water. This height varies in different latitudes and at different seasons. It increases as we approach the equator, and diminishes as we go towards the poles. It is higher, also, at any given place, in summer than in winter. It is moreover, higher when the surface of the ground below is elevated, like the table land of Mexico. At a mean the cold increases at the rate of about 1° for every 300 feet of elevation. In addition to the above it ought to be mentioned, that the tops of mountains part with the heat they receive from the sun more

readily on account of the radiation taking place more freely in a rarer medium, and where there are few objects to send the rays back again.

Continued on page 142.)

MISCELLANIES.

Origin of the Bat's Wing Gas Burner.-This excellent method of producing a large light with a small expenditure of gas, was discovered by accident, and shows the trivial circumstances from which the greatest improvements often arise. A brass-founder, who wished to exhibit to a friend the production of gas on a small scale, when it first came into use, had at hand only a burner, whose hole had accidently been stopped up; and not having any instrument at the time to unstop it, he in haste took hold of a saw which lay by him, and made a cross cut through the hole. When this was tried, he found to his great joy, that it produced the most brilliant effect; and being a collector of animals, he instantly compared it to the wing of a bat, which name the burner has kept ever since. His friends were anxious he should secure an interest in it by a patent, but he generously gave it to the trade at large.

The Spider. Of all the insect tribes which come beneath the bane of vulgar prejudice, this is assuredly the most curious. First, the Barbary

spider, which is as big as a man's thumb. This singular creature carries its children in a bag like a gipsy. During their nonage the young folks reside there altogether, coming out occasionally for recreation. In requital for this kindness on the part of their nurse, the young spiders, when they are full grown, become mortal foes to the parent, attack her with violence, and if they are conquerors dispose of the body as a fit subject for their next meal. Then there is the American spider, covered all over with hair, which is so large as to be able to destroy small birds, and afterwards devour them; and also the common spider, whose body looks like a couple of peninsulas with a little isthmus (its back) between.

Kemoval of Great Weights.-Is it not ridiculous that, in spite of our knowledge of the mechanical powers, nations in a semi-barbarous state should perform with ease and alacrity what our engineers fail to do? The famous gun Malik-e-meidan, or Lord of the Field, at Berjapoor, 14 feet 9 inches in length, with a bore of the diameter of 2 feet 5 inches, and 14 inches thickness of metal, was originally cast at Ahmednuggur, 150 miles from where it now lies, on one of the bastions of the wall of Berjapoor, yet the project of transporting it to England was, on account of its size and weight, given up in despair, as was also the case with the great gun at Agra, which has lately been blown to pieces. A large party of sailors and laborers were employed for a fortnight at Rangoon, in Birma, in transporting the large bell attached to the famous temple, a distance of a few yards to the river, in the middle of which they managed to deposit it, instead of in a brig as was intended. Despairing of success it was delivered over to the Birmese, who, in the course of three days, raised it from the bed of the river to its former situation in the temple. Indelible Ink prepared from Vanadium.-The following account is given by Berzelius, of a new and almost indelible ink, applicable to all common

purposes, which he has prepared from the recently discovered metal, vanadium. The vanadates of ammonia, that is the combinations of the acid, formed by this metal with oxygen, united to the alkali ammonia, when mixed with infusion of galls, form a black liquid, which is the best writing ink that can be used. The quantity of salt necessary for a perfectly black ink is so small, that it will be not worth considering, when vanadium is more generally known. The writing obtained with this ink is perfectly black. Acids render it blue, but do not obliterate it like common writing ink; the alkalies when sufficiently diluted not to act upon the paper, do not dissolve it, and chlorine, which destroys the black color, does not, however, efface the writing, even when water is afterwards suffered to run over it. In a word, if this ink is not perfectly indelible, it strongly resists reagents, which instantly cause common ink. to disappear; added to which, it is blacker and flows better, because it consists of a solution, and not of a precipitate suspended in a solution of gum. It remains to be proved what the effects of time will be upon it.

To remove a Hard Coating or Crust from Glass and Porcelain Vessels.-It often happens that glass vessels, used as pots for flowers and other purposes, receive an unsightly deposit or crust, hard to be removed by scouring or rubbing. The best method to take it off, is to wash it with a little dilute muriatic acid. This acts upon it, and loosens it very speedily.-Journal des Connaissances Usuelles.

Scotch Method of Preserving Eggs.-Dip them, during one or two minutes in boiling water. The white of the egg then forms a kind of membrance, which envelopes the interior, and defends it from the air. This method is preferable to the varnish proposed by Reaumur.

Substitute for India Ink.-Boil in water, some parchment or pieces of fine gloves, until it is reduced to a paste. Apply to its surface while still warm, a porcelain dish which has been held over a smoking lamp: the lamp-black which adheres to it, will become detached and mingle with the paste or glue. Repeat the operation until the composition has acquired the requisite color. It is not necessary to grind it. It flows as freely from the pencil as India ink, and has the same transparency.

QUERIES.

98. What is the cause of the rotary motion acquired by a watch glass when placed on an inclined looking glass, in its progress to the bottom? Answered on page 413.

99.-To what extent has carburetted hydrogen been compressed, has it ever yet been reduced to a solid or liquid, and if so, does it resume the aeriform state, on the pressure being removed? Answered on page 312.

100. Is there any point in the mandril of a lathe which remains stationary, while the mandril revolves? Answe, ed on page 176.

101.-What is the principle of the quicksilver bats? Answered on page 176.

102.-What is the difference between sheet and forked lightning, and the cause of that difference? Answered on page 207.

103. Is there any rule for geometrically trisecting any rectilineal angle? Answered on page 207.

S

104.-What sort of gum or glue do modellers in cirard board use? Answered on page 160.

105.-How is hair sorted into lengths, and cleansed? Answered on page 359.

106.-What is the reason that a drop of glass n being broken at the smaller end, flies into dust? Answered or page 312. 107.-Why may there not be invented a perpetual motion, and what is the nearest approach to it yet known? Answered on page 194. 108.-Why is snow white? Answered on page

20

t

TURNING.

THERE is, perhaps, no contrivance with which human ingenuity has aided the dexterity of the mechanic more entitled to our admiration than the lathe especially when we take into account all the improvements it has undergone, from its simplest and most ancient form in the potter's wheel, to that adaptation of varied and complex mechanism, by which not merely circular turning of the most beautiful and accurate description, but exquisite figure-work, and complicated geometrical designs, depending upon the eccentric and cycloidal movements, are daily produced.

The operation of turning differs very essentially from most others, in the circumstance, that the matter operated upon is put in motion by the machine, and is wrought by means of edge tools, presented to it, and held fast; whilst in most others the work is fixed, and the tool put in motion. In ordinary turning, the work is made to revolve on a stationary straight line as an axis, while an edge tool, set ready to the outside of the substance in a circumvolution thereof, cuts off all the parts which lie farthest from the axis, and makes the outside of that substance concentric with the axis. In this case, any section of the work made at right angles to the work will be of a circular figure; but there are methods of turning ellipses and various other curves, distinguished by the name of engine-turning. [SECOND EDITION.]

Lathes are made in a great variety of forms, and put in motion by different means; they are called centre-lathes where the work is supported at both ends; mandril, spindle, or chuck lathes, when the work is fixed at the projecting extremity of a spindle. From different methods of putting them in motion, they are called pole-lathes, and hand-wheel lathes, or foot-lathes; for great works they are turned by horses, and water-wheels, but more generally by steam-engines. The lathes used by wood turners are usually made of wood in a simple form, and are called bed-lathes; the same kind will serve for turning iron and brass: but the best work in metal is always done in iron lathes, which are usually made with a triangular bar, and are called bar-lathes. Small ones, for the use of watch-makers, are denominated turn-benches; but there is no essential distinction between these and the centre lathes, except in regard to size, and that they are made in metal instead of wood, and the workmanship being more accurate and better finished.

The Centre Lathe is of all these machines the most simple. It consists of two upright blocks, or as they are called puppets, one of them moveable backwards and forwards, and both of them bearing a screw, which passes through them horizontally, and in a line with each other; these screws are pointed; and between the points the work to be turned is fixed, while a circular motion is given to it by a string passed once or twice round the work,

and fastened below to a treadle, the upper end of it going over a pulley, and having a weight attached, or else fastened to an elastic pole, which draws the string back again when it has been forced downwards by the treadle. This lathe is now but little used, as it is not applicable to the general purposes of the turner, it being impossible to turn any delicate work, or that which is required to be hollow, even to turn a disk by means of the centre lathe is difficult, if not impossible.

The Foot Lathe, with Mandril and Collar.-A lathe of this kind serves equally well for centre work and the more delicate and beautiful specimens of the art, whether of ivory, metal, or wood, and is that almost universally employed by the amateur, as well as the professed artizan. The introductory engraving, and following description which refers to it, will show the simplest construction, and being made almost wholly of wood, the amateur will have but little difficulty in making a great part of it himself, should it be desirable.

The bed of the lathe consists of two beams or cheeks fixed parallel to each other, and leaving a space of about 1 inch between them. The cheeks may be 3 feet long, 5 inches deep, and 2 inches thick, and made of yellow deal, or still better of oak. The bed of the lathe is supported by legs at the end, properly framed together, so as to bear the wheel, &c. afterwards to be mentioned.

A is the mandril, the most important part of the lathe, it is usually fixed in a strong iron frame or bed, totally distinct from the wooden bed of the lathe itself, as is shown in the engraving. It consists of a spindle fixed in this iron frame, in a horizontal direction, made of iron, but bearing a steel point at one end, where it is supported by the screw K, and furnished at the other end or nose of the mandril, as it is called, with a screw L., to which screw, the work is afterwards to be attached by means of chucks, &c. Where it passes the inner leg of the iron support it works into a correctly turned steel collar, thus the spindle is capable of motion readily around its centre, but in no other direction. To give it this motion the spindle is furnished with a wheel of three or more differently sized grooves, over one of which a rope or catgut passes. This, which is called the lathe band, extends over a fly wheel placed beneath the bed, seen as connected with the axis and cranks F. The flywheel, which must be of considerable weight, is so much larger than the mandril wheel above, as to cause the latter to revolve many times during one of its own revolutions. The cranks are connected by bent iron links to the treadle G. The motion is therefore communicated from the workman's foot to the treadle G.; it passes through means of the cranks to the axis and wheel F, and then onwards to the mandril, and supposing a piece of wood be fastened to the screw L, it will of course turn round with equal velocity to the mandril with which it is

in unison.

The spindle then which forms the axis, must be at the same height above the bed as the nose of the mandril and ought to run in a correct line with it, and be so accurately fitted into its socket as not to shake in the smallest degree in the after operation.

Figure 2, and B, Fig. 1, is the rest, and is intended to support the tools when in use. It is formed of two parts, both of iron. The lower part has a hollow socket in front, and a divided or forked foot, which enables it to be drawn backwards and forwards, that it may be set to any distance from the central axis, to accommodate it to the diameter of the work and the convenience of the workman. It is connected with the bed of the lathe by the screw H. The upper part of the rest consists of a round iron bolt, fitting the socket of the lower portion. On the top of this a cross piece made smooth at top, upon which the tool is rested. It will be seen that by these simple movements the upper part may be fixed to any height, and in any position, by means of the smaller screw in the socket, while it moves to the requisite distance and situation by the screw below.

Practical observations on chucks, tools, and mode of operating will form the subject of future remarks, which we are induced the more readily to give, because there is no work on turning in the language, except one by Ibbetson, which is upon one branch only, and intended rather to give an account of a chuck of his invention, than to explain the general principles of the art.

LUMINOUS ANIMALS AND INSECTS.

THE remarkable property of emitting light during life, is only met with amongst animals of the four last classes of modern naturalists, viz. mollusca, insects, worms, and zoophytes.

The mollusca and worms contain each but a single luminous species; the pholas dactylus in the one,

and the nereis noctiluca in the other.

The

Some species yield light in the eight following genera of insects; elata, lampyris, fulgora, pausus, scolopendra, cancer, lynceus, and limulus. luminous species of the genera lampyrus and fulgora, are more numerous than is generally supposed, if we may judge from the appearance of luminous organs to be seen in dried specimens. Amongst zoophytes we find that the genera medusa, bereo, and pennatula, contain species which afford light.

The only animals which appear to possess or

minous species of lampyrus, elator, fulgora, and

pausus.

The light of the lampyrides, (glow worms,) is known to proceed from some of the last rings of the