The Boy's Playbook of Science Part 30

[Ill.u.s.tration: Fig. 230. Ga.s.siott's Cascade.]

_Ninth Experiment._

If a piece of wood five inches long and half an inch square is placed on the table of the discharger, and one wire brought on to the top edge and the other approached to within three inches of it, and touching the wood, and the s.p.a.ce between them moistened with the strongest nitric acid, a curious effect is visible from the creeping along of the fire, which gradually carbonizes and burns the wood. (Fig. 231.)

[Ill.u.s.tration: Fig. 231. Burning the piece of wood moistened with the strongest nitric acid.]

[Page 239]

_Tenth Experiment._

A gla.s.s plate wetted with gum, and then sprinkled with various filings of iron, zinc, lead, copper, &c., produces a very pretty effect of deflagration as one of the conducting wires is moved over its surface, the other of course being in contact with the plate. The gum quickly dries by putting the plate in a moderately-heated oven.

_Eleventh Experiment._

When the continuous discharges from the Leyden jar are made to pa.s.s through the centre of a large lump of crystal of alum, blue vitriol, or ferroprussiate of potash, &c., the whole of the crystal is beautifully lighted up during the pa.s.sage of the electricity from one wire of the discharger to the other. (Fig. 232.)

[Ill.u.s.tration: Fig. 232. A. The Leyden jar. B. Large lump of alum, with a hole bored through it in a line with C D. The discharging wires are brought within three-eighths of an inch of each other, and the whole crystal is lighted up with the brilliant electric sparks.]

_Twelfth Experiment._

When a piece of paper slightly damped is placed between the wires of the discharger, the spark is increased to a much greater length, on account of the conducting power of the water contained in the pores of the paper; and taking all things into consideration, the author considers he has witnessed the grandest effects from the coil invented and constructed by Mr. Hearder, the talented lecturer and electrician of the West of England.

_Thirteenth Experiment._

Electro-magnetic coil machines have been employed for a very considerable time in alleviating certain of "the ills which flesh is heir to," [Page 240] by the administration of shocks. These may be so regulated as to be hardly perceptible, or may be so powerful that the pain becomes absolutely intolerable.

These coils are now made self-acting, and consist of two coils of covered and insulated wire wound round a bundle of soft-iron wires, with the necessary connecting screws for the voltaic battery. The contact with the battery is made and broken with great rapidity by a simple form of break, consisting of a tinned disc of iron held by a spring over the axis of the bundle of iron wires; and the continual noise of the break, which is alternately attracted down to the bundle and brought back by the spring, when the coil is in contact with the battery, demonstrates (without the pain of taking the shock) when the instrument is in full working order.

The coil machine is not only useful in a medical point of view, but when properly arranged offers a good reception to a run-away bellringer, and is an excellent preventive against illicit attempts at cheap rides by small boys.

[Ill.u.s.tration: Fig. 233. Boy, _evidently shocked_, behind doctor's carriage provided with a small coil machine.]

[Page 241]

CHAPTER XIX.

MAGNETO-ELECTRICITY.

[Ill.u.s.tration: Fig. 234. Clarke's magneto-electrical machine.]

The correlation of the physical forces, heat, light, electricity, magnetism, and motion, is one of the most interesting subjects for study that can be suggested to the lover of science. The examination of the precise meaning of the term correlation, so ably considered by Professor Grove, indicates a necessary mutual or reciprocal dependence of one force on the other. Thus, electricity will produce heat, and _vice versa_; motion, such as friction, produces electricity, and the latter, by its attraction and repulsion, establishes itself as a source of motion. Electricity produces light, also magnetism, and contrariwise light is said to possess [Page 242] the power of magnetizing steel, whilst magnetism again produces light and electricity. Such are the intimate connexions that exist between these imponderable agents, and we may trace cause and effect and its reversal amongst these forces, until the mind is lost in the examination of the bewildering mazes, and is content to return to the beaten track and work out experimentally the practical truths. We have had occasion to notice in another part of this playbook the fact that a current of electricity causes the evolution of magnetism in its pa.s.sage through various conducting media, and the truth has been specially ill.u.s.trated by the various experiments in the chapter devoted to electro-magnetism. In commencing this portion of electrical science, we have no new terms to coin for the t.i.tle of the discourse, as we merely reverse the other when we examine the nature and peculiarities of

MAGNETO-ELECTRICITY.

The source of the power must necessarily be a bar or horse-shoe shaped piece of steel permanently endowed with magnetism. If the former is thrust into a cylinder of wood or pasteboard, around which coils of covered copper wire have been carefully wound, so that the extremities communicate with a galvanometer, an immediate deflection of the needle occurs, which, however, quickly returns to its first position, but is again deflected in the opposite direction on the withdrawal of the steel magnet from the coil of copper wire. (Fig. 235.)

[Ill.u.s.tration: Fig. 235. A B. Coil of copper wire. C. Permanent bar magnet placed inside the coil, when the galvanometer needle, D, is deflected.]

The rapid entrance and exit of the steel magnet in the helix of copper wire would be insufficient to produce any quant.i.ty of electricity, and the ingenuity of man has been taxed to arrange a method by which a magnet may be suddenly formed and destroyed inside a coil of insulated copper wire. The difficulty, however, has been surmounted by several ingenious contrivances, based on the principles first discovered by Faraday; and the one especially to be noticed is the revolution of a coil of copper wire enclosing a piece of soft iron, called the _armature_, before the poles of a powerful magnet. The first machine was invented [Page 243] by M. Hypolyte Pixii, of Paris, and in 1833, Mr.

Saxton improved upon this machine, and three years afterwards, Mr. E. M.

Clarke described a very ingenious modification of the electro-magnetic machine, which is depicted at page 241 of this chapter. In this picture, the letter A is the permanent fixed horse-shoe magnets, which are very appropriately termed the _battery_ magnets, because they take the position that would otherwise be occupied by a voltaic battery, and they are indeed the prime source of the electrical power that is evoked. D is the intensity _armature_ which screws into a bra.s.s mandril seated between the poles of the magnets A, motion being communicated to it by the multiplying wheel, E. This armature or _inductor_ has two coils of fine insulated copper wire of 1500 yards in length, coiled on its cylinders, the commencement of each coil being soldered to the bar D, from which projects a bra.s.s stem, also soldered into D, carrying the break-piece H, which is made fast in any position by a small binding-screw in a hollow bra.s.s cylinder to which the other terminations of the coils, F F, are soldered, these being insulated by a piece of hard wood attached to the bra.s.s stem. O is an iron wire spring pressing against one end of the hollow bra.s.s cylinder; P is a square bra.s.s pillar; Q is a metal spring that rubs gently on the break-piece H; T is a copper wire for connecting the bra.s.s pieces with the wood L between them, and out of which P and O pa.s.s; R R are two handles of bra.s.s with metallic wires, the end of one being inserted into either of the bra.s.s pieces connected with P and O, and the other into the bra.s.s stem that carries the break-piece H, delivers a most severe shock directly the wheel is set in motion.

In Saxton's electro-magnetic machine, the permanent steel magnets are placed horizontally instead of perpendicularly, and are composed of six or more horse-shoe-shaped pieces of steel. The armatures, or inductors, or electro-magnets (for they consist of pieces of soft round iron with wire wound round them), are two in number, and are adapted to exhibit either _quant.i.ty_ or _intensity_ effects. The quant.i.ty armature is constructed of stout iron, and covered with thick insulating wire. The intensity armature is made of slighter iron, and covered with from one thousand to two thousand yards of fine copper wire coated with silk. The _quant.i.ty_ armature is intended for the exhibition of results similar to those which are procurable from a voltaic battery, such as the magnetic spark, inducing magnetism in soft iron, heating platinum wire. The intensity armature is employed for the chemical decomposition of water and other bodies, and likewise for the administration of those terrible blows to the nervous system which cause strong men of the mildest deportment to become painfully excited, and to make those e.j.a.c.u.l.a.t.i.o.ns which are so peculiar to the genus John Bull.

EXPERIMENTS WITH THE MAGNETO-ELECTRIC MACHINE.

_First Experiment._

The decomposition of water by the pa.s.sage of electricity from one platinum plate to another, has already been ill.u.s.trated at page 198.

The [Page 244] same fact may likewise be displayed by the following arrangement of the machine. (Fig. 236.)

[Ill.u.s.tration: Fig. 236. A. Apparatus for decomposing water and collecting the gases separately. B B. Wires proceeding from the machine at M, N. Q, works on the single break, H.]

_Second Experiment._

The electric light obtained by the pa.s.sage of the electricity from the battery through the charcoal points, is also an effect that can be produced by magneto-electric machines, the wires leading from the points A B being insulated by gla.s.s handles, and placed in the holes M N. (Fig.

237.)

[Ill.u.s.tration: Fig. 237. The electric light obtained from the magneto machine.]

[Page 245]

_Third Experiment._

The scintillation of iron wire is one of the most pleasing experiments with this apparatus, and is performed by pressing gently one end of a piece of thin iron wire (attached by means of a binding-screw to the upright bar A) against the armature, D. (Fig. 238.)

[Ill.u.s.tration: Fig. 238. Deflagration of iron wire.]

_Fourth Experiment._

The combustion of ether or other inflammable spirit may also be demonstrated with the aid of this powerful apparatus, and the arrangement, in common with the others employed by Mr. Clarke, is shown in Fig. 239.