The Magazine of Science, and Schools of Art

The tube containing the mirror and lens can be turned round by a rod within, and the inclination of the mirror changed, so as to introduce objects in any part of the horizon.

The Box Camera is still more portable, and may be constructed with yet greater facility, as follows:Procure a box 12 inches long, 6 wide, and 4 deep. In the centre of one end place a lens, as before, (a common double convex lens, of about 10 inch focus, and which costs 6d., will do very well,) and inside the box at the other end a piece of looking glass, at an angle of 45°, that is, half way between the vertical and the horizontal line, to reflect the objects upwards. That these may become visible, a part of the top of the box over the looking glass is cut away, and its place supplied with a piece of ground glass, the ground side to be placed uppermost. The instrument is now complete, except a blind or shield is required to keep extraneous light from falling upon the picture. This is effected easily, by the piece of wood which was removed from the top to make way for the glass being still suffered to remain suspended over it at a convenient distance.

In the above cut A is the lens, B the looking glass reflector, and C the plate of ground glass upon which the view is made apparent, and D the shield; the latter is capable of being moved up and down, to shut off as much light as may be advisable, and the lens is sometimes made to slide in a tube, in order that its focus may be better adjusted to the reflector, and that the objects depicted may be rendered as clear and vivid as possible. The action of the instrument will be easily understood; the light from the objects around is thrown upon A, they pass onwards to the reflector B, and are cast upwards to the lower side of C. This being transparent, they are seen on its upper side by a person looking into the instrument.

ELECTRICITY.

ELECTRICITY of all sciences has during the present century made nost rapid strides, and stands preeminent in explaining the grander and more important universal phenomena of nature. It gives an explanation of the workings of a subtle and elastic fluid, called the electric fluid, which is distributed throughout all creation, remaining while at rest imperceptible to us, but when disturbed by mechanical friction, heat, or chemical action, producing all those effects called Electrical and Galvanic; perhaps Magnetic also.

The lightning, the Aurora Borealis, the waterspout, the whirlwind, the rolling pillars of sand of the desert, are but a few among the numerous effects of that powerful action of the fluid produced by friction, and which is usually called free electricity; frictional electricity; or electricity of tention, a science which from its first discovery has always been popular, not merely from its utility, but from the extreme beauty, and infinite variety of the experiments which illustrate it, most of which may be performed with but ordinary trouble, and at little danger or capense.

Singular it is that a universal fluid such as this, should not have been known to exist until about 200 years ago, yet electrical appearances were then first observed, and the more surprising, as there is scarcely an action we can do, and scarcely a motion of inanimate nature can take place, be it mechanical or chemical, which does not in some manner disturb the equilibrium of the electric fluid. The impinging of cloud upon cloud-the evaporation of moisture from the earth's surface-the fall of rain-the rolling of the ocean-are all stupendous electrical machines, and it requires only a concurrence of favorable circumstances to render the disturbance perceptible to one or more of our senses.

The proof of the universality of the fluid, and the facility of its disturbance will be evident by the following experiments, which are performed without the aid of a machine of any kind.

ON EXCITATION.

Er. 1.-Take a piece of common brown paper, about the size of an octavo book, hold it before the fire till quite dry and hot, and draw it briskly under the arm several times, so as to rub it on both sides at once by the coat. The paper will now be found so powerfully electrical, that if placed against a wainscot or the papered wall of a room, it will remain there for some minutes without falling.

Ex. 2.-If while the paper remain fixed to the wall, a light fleecy feather be placed against it, it will adhere to the paper in the same way as the paper adheres to the wall.

Ex. 3.-If the paper be again warmed, excited, and hung up, a thread attached to one corner of it, it will hold up several feathers on each side; should these fall off from different sides at the same time, they will cling together very strongly, and if after a minute they be all shook off together, they will fly to one another in a most extraordinary manner.

Ex. 4.-Heat and excite the paper as before, lay on a table, and place upon it a ball, about the size of a pea, made of elder pith; this ball will immediately run across the paper, and if a needle be pointed towards it, the ball will again travel to another part, and so on for a considerable time.

Ec. 5.-Rub the end of a stick of common sealing wax, or a piece of amber, on the coat-sleeve, when it readily attracts from the table, bran, filaments of linen, minute scraps of paper, &c., and holds them suspended in the air.

Ex. 6.-Take two pieces of white paper, warm them at the fire, place them upon each other on a table or book, and rub strongly the upper paper with a piece of India rubber; the paper will now be found strongly electrical, so as to adhere together with such force that it requires some trouble to separate them, and when separated and then made to approach each other again, they will immediately rush together a second time. If they be separated from each other in the dark, a flash of electrical light will be seen between them, most frequently accompanied with a cracking noise, which is the electric spark, and thus showing the electric fluid in sufficient quantity to be perceptible to the eye and ear.

Ex. 7.-Take two silk ribbons, one black, the other white, each about three feet long; warm them at the fire, holding them up flat against each other with one hand, and draw the thumb and fingers of the other hand briskly over them several times; they will thus become powerfully excited, and although the upper ends of the ribbons be forcibly separated,

THIS instrument, the object of the above engraving, and present description, was invented by Friar Bacon more than five hundred years ago. It is of such simple construction as to be easily understood, and represents the objects subjected to it in all their vivid colors, and with so unerring a fidelity, that it has always been a favorite amusement to view its varied and animating pictures. The following is an explanation of its construction :

The engraving represents a room, into which the light penetrates only through the top at C. The rays of light A, tinged with the color of the objects reflected, pass through a hole in the side of the upper part of the instrument, and strike upon the looking-glass or reflector B, from this they are cast down upon the double convex lens C, fixed in the cross partition F G-here they diverge in proportion to the focus of the lens, and passing onwards are at last met by the white table below, D E, where the original objects are vividly depicted. The accuracy

of proportion and truth of perspective will, however, not be ensured by a flat table, as will be evident upon considering that on a flat surface the rays of light passing through the lens will be shorter in the centre of the picture than those that reach the sides, (as is seen in the figure ;) in consequence, the representation will be somewhat distorted, and also more brilliant towards the centre than near the circumference of the field of view. To remedy this, two methods suggest themselves; one, to have the table DE part of a hollow sphere of a radius according to the distance of the lens. This arrangement has a serious objection in delineating the objects represented, because of the impossibility of laying a sheet of paper on a spherical body. An alteration, therefore, of the lens itself is the only remaining resource; if this, instead of being double convex, be a meniscus glass, (that is, like a watch glass, thick in the middle,) having its concave side next the object, and if radii of the two surfaces be as 1 to 2, the outer rays will be rendered longer than those near the centre, and by this means the correctness and brilliancy of the picture will be greatly increased.

The upper part of the instrument is made to turn

round upon a groove at F G, by which means the reflector may be directed to any side of the landscape; the reflector B is also moveable on a joint near the centre of its sides, like a dressing-glass, and thus it is made to reflect either distant or near objects. The hole in the side, at the top, may have a convex lens inserted in it, but although by this contrivance a larger field of view is obtained, trilliancy is lost in equal proportion.

Portable Camera.-This instrument has many modifications: the above construction may be adapted to a large conical box, there being one hole or more cut in the side of it, to view the objects represented on the table within. A very convenient portable camera obscura for drawing landscapes or other objects is shown in the following figure,

where A is the meniscus with its concave side uppermost, and the radius of its convex surface being to the radius of its concave surface as 5 to 8, and B a plane metallic speculum, inclined at an angle of 45° to the horizon, to reflect the landscape down wards through the lens A. The draughtsman introduces his hand with the pencil through an opening in the side, made in such a manner as to allow no light to fall upon the picture, which is exhibited on the paper at C, a cloth covering over the man.

The tube containing the mirror and lens can be turned round by a rod within, and the inclination of the mirror changed, so as to introduce objects in any part of the horizon.

ELECTRICITY.

ELECTRICITY of all sciences has during the present century made most rapid strides, and stands preeminent in explaining the grander and more important universal phenomena of nature. It gives an explanation of the workings of a subtle and elastic fluid, called the electric fluid, which is distributed throughout all creation, remaining while at rest imperceptible to us, but when disturbed by mechanical friction, heat, or chemical action, producing all those effects called Electrical and Galvanic; perhaps Magnetic also.

The proof of the universality of the fluid, and the facility of its disturbance will be evident by the following experiments, which are performed without the aid of a machine of any kind.

ON EXCITATION.

Ex. 2.-If while the paper remain fixed to the wall, a light fleecy feather be placed against it, it will adhere to the paper in the same way as the paper

adheres to the wall.

Ex. 5.-Rub the end of a stick of common sealing wax, or a piece of amber, on the coat-sleeve, when it readily attracts from the table, bran, filaments of linen, minute scraps of paper, &c., and holds them suspended in the air.

to the distance of a foot or more, the lower ends ! will still cling together.

Ex. 8. Another instance of electric repulsion is seen when a bunch of long hair is combed before a fire, each particular hair will stand on end," and get as far as possible from its neighbour.

Ex. 9.-Support a pane of glass, (first warmed,) upon two books, one at each end-place some bran underneath it, and rub the upper side with a warm black silk handkerchief or a piece of flannel-the bran will now fly and dance up and down with much rapidity.

Obs. In this way electric attraction was first discovered. A glazier, cleaning some window. sashes lying on a table, observed the small particles of whiting underneath to jump up and down; but it was long afterwards before the cause of this was known to be electrical.

(Continued on page 10.)

A trial was made with a tube of one inch in diameter, very nearly two miles in length, returning upon itself, so that both ends of the tube were brought to one place the compression applied at one end, was equal to a column of seven inches of water; and the effect on the index at the other end appeared in fifteen seconds of time.

Laws have been propounded by eminent men on the expenditure of æriform fluids through conduit pipes, and of the resistance of the pipes; but these are not strictly applicable to the present question. Under all circumstances, it seems desirable experiments on a practical scale, at extended distances, should be resorted to, as the most satisfactory guide, for carrying into effect telegraphic communications of this kind.

The following is a representation of the instru ment of Mr. Crosley, which will be easily under. stood from the above description.

PNEUMATIC TELEGRAPH.

A PNEUMATIC telegraph has been invented by Mr. S. Crosley, an operative model of which is to be seen at the Polytechnic Institution, Regent Street. Atmospheric air is the conducting agent employed in its operation. The air is isolated by a tube extending from one station to another; each extremity of the tube being connected with a vessel containing a small volume of air in direct communication with the air in the tube. This vessel is employed as a reservoir to compensate for any increase or diminution which must necessarily arise from compression, or from changes in the temperature of the air, and for supplying any casual loss by leakage; the vessel must, therefore, be capable of enlargement and contraction in its capacity, after the manner of bellows, or as a gas-holder, by immersion in water, so as to maintain, uniformly, any particular degree of compression which may be given to it.

It will be evident to every one acquainted with the physical properties of atmospheric air, that if any certain degree of compression be produced and maintained in the reservoir, at one station, equilibrium will rapidly succeed, and the same degree of compression will extend to the opposite station, where it will become visible to an observer by means of a pressure index.

Thus, with ten weights, producing ten different degrees of compression, distinguished from each other numerically, and having a pressure index at the opposite station, marked by corresponding figures, any telegraphic numbers may be transmitted, referring in the usual way to a code of signals, which may be adapted to various purposes and to any language. The only manipulation is that of placing a weight of the required figure upon the collapsing vessel at either station, and the same figure will be represented by the index at the opposite station.

Previously to making a signal, the attention of the person, whose duty it is to observe it, is arrested by means of a preparatory signal.

The communication between one extremity and the other may be made known at intermediate stations, by connecting with the air tube indexes, corresponding with those at the extremities; but in order to avoid the necessity for additional sounding apparatus, which would retard the communications between the extremities, it would be necessary to limit such intermediate communications to stated periods, so that an observer might be in attendance.

A is a cylinder of air at one extremity of the line, C is supposed to be a distant station, B the tube which connects these places, D the index at one of the stations; each cylinder or air vessel contains a little water, with a pipe below the surface of it. When the air at one end is compressed, the com. pression extends equally throughout the whole extent of the instrument, and pressing upon the surface of the water, raises it in the gages or index tubes equally at all the stations; these being numbered, and the numbers made representative of certain previously arranged signals, indication is of course readily communicated. F is a funnel to supply the water, to produce the proper adjustment at first, and also if it should become incorrect by leakage or accident. G a pipe leading to a further station, capable of being acted upon at the same time as the second, or by a cock each may be shut off as required.-Phil. Mag.

THE NOVEMBER METEORS. SHOOTING stars and meteors burst from the clear azure sky, and darting along the heavens, are extinguished without leaving any residuum, except a vapour-like smoke, and generally without noise. Their parallax shows them to be very high in the atmosphere, sometimes even beyond its supposed limit, and the direction of their motion is for the most part diametrically opposite to the motion of the earth in its orbit. The astonishing multitudes of shooting stars and fire balls, that have appeared

within these few years, at stated periods, over the American continent, and other parts of the globe, warrant the conclusion, that there are myriads of bodies revolving in groups round the sun, which only become visible when inflamed by entering our atmosphere.

One of these groups seems to meet the earth in its annual revolution on the 12th and 13th of November. Several very remarkable instances have occurred.

On the morning of the 12th of November, 1799, thousands of shooting stars, mixed with large meteors, illuminated the heavens for many hours over the whole continent of America, from Brazil to Labrador; it extended to Greenland and even Germany. Meteoric showers were seen off the coast of Spain, and in the Ohio country, on the morning of the 13th of November, 1831: and during many hours on the morning of 13th of November, 1832, prodigious multitudes of shooting stars and meteors fell at Mocha on the Red Sea, in the Atlantic, in Switzerland, and at many places in England. But by much the most splendid meteoric shower on record began at nine o'clock in the evening of the 12th of November, 1833, and lasted till sunrise next morning. It extended from Niagara and the northern lakes of America to the south of Jamaica, and from 61 degrees of longitude in the Atlantic to 100 degrees of longitude in central Mexico. Shooting stars and meteors, of the apparent size of Jupiter, Venus, and even the full moon, darted in myriads towards the horizon, as if every star in the heavens had started from its sphere. They are described as having been frequent as flakes of snow in a snow storm, and to have been seen with equal brilliancy over the greater part of the continent of North America.

Those who witnessed this grand spectacle were surprised to see that every one of the luminous bodies, without exception, moved in lines which converged to one point in the heavens: none of them started from that point; but their paths, when traced backwards, met in it like rays in a focus, and the manner of their fall showed that they descended from it in nearly parallel straight lines towards the earth.

By far the most extraordinary part of the whole phenomenon is, that this radiant point was observed to remain stationary near one of the stars of the Lion for more than two hours and a half, which proved the source of the meteoric shower to be altogether independent of the earth's rotation, and its parallax showed it to be far above the atmosphere.

As a body could not be actually at rest in that position, the group must either have been moving round the earth or the sun. Had it been moving round the earth, the course of the meteors would have been tangential to its surface, whereas they fell almost perpendicularly, so that the earth in its annual revolution must have met with the group. The bodies that were nearest must have been attracted towards the earth by its gravity, and as they were estimated to move at the rate of fourteen miles in a second, they must have taken fire on entering our atmosphere, and been consumed in their passage through it.

As all the circumstances of the phenomenon were similar on the same day and during the same hours in 1832, and as extraordinary flights of shooting stars were seen at many places, both in Europe and America, on the 13th of November, 1834, and also

on the same day of every succeeding year, tending also from a fixed point in the constellation Leo-it has been conjectured with much apparent probability that this group of bodies performs its revolution round the sun in a period of about 182 days, in an elliptic orbit, whose major axis is 119 millions of miles; and that its aphelion distance, when it comes in contact with the earth's atmosphere, is about 95 millions of miles, or nearly the same with the mean distance of the earth from the sun. This body must have met with disturbance after 1799, which prevented it from encountering the earth for 32 years, and it may again deviate from its path from the same cause. How far these conjectures respecting the form and position of the orbit correspond with observation, time alone will show; but every circumstance tends more and more to confirm the existence of a zone composed of millions of little bodies, whose orbits meet the plane of the ecliptic towards the point which the earth occupies each year between the 11th and 13th of November. Thus, as M. Arago observes, a new planetary world is about to be revealed to us.-Mrs. Somerville.

ON SKINNING, PRESERVING, AND STUFFING BIRDS, FOR CABINETS. HAVE ready for use some cotton wadding, some burnt alum in powder, a blunt moderately-large wire, about four inches long, and a pair of scissors : and if the stuffing and mounting are to be proceeded with immediately some tow, some iron wire, with a file to point it, a long tapering brad-awl, and various sprigs of wood will also be necessary.

In proceeding to skin the bird, it should be laid on its back with the feathers of the breast separated to the right and left, when a broad interval will be discovered reaching from the top to the bottom of the breast-bone. The scissors must be inserted at the point of the bone,and cut the outer skin from thence to the vent, taking care not to penetrate so deep as the flesh, or upon the inner skin which covers the intestines. The skin will then be easily separated from the flesh, in larger specimens by the fingers, in smaller by passing the blunt wire between the skin and the body observing at all times to push the skin rather than pull it, which is very likely to tear, or to stretch out of shape, the legs may then be slipped up, and are to be cut through at the middle of the thighbone, and all the flesh upon the skin carefully cut away, and the clean bone rubbed with the burnt alum. This must also be rubbed over every part of the skin as separated from the flesh, in order to prevent soiling it with blood, and to preserve it afterwards from the depredations of insects.

The skinning is now to be continued to the rump, which is cut off close, but so as not to injure the tail feathers. The lower part of the body being now loosened, the skin may be drawn back till the wings prevent its being drawn further. The wings are then to be drawn out and cut off at the shoulder, the upper bones being cleaned and rubbed as the legs had been before. The skin is still drawn back, (but not so as to stretch the neck,) until the base of the skull is laid bare, when the whole body is cut away close to the skull, and also a part of the back of the skull itself, in order to take out, through the opening of the brains, the eyes, and any fleshy part not wanted in the stuffing. When the skin is wiped dry in every part, and examined, in order to remove any particle of flesh or fat that may adhere to it, the operation of skinning is complete, and nothing

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