The Gyroscope, though now an instrument common and familiar to all students, is none the less the subject of a problem, the solution of which is still to seek. It has indeed been entitled the paradox of mechanics; for though it depends on gravitation, gravitation yet appears indifferent to it. In order to render the operation of the Gyroscope as continuous as possible, so as to facilitate the profound study of its working, and also to unite another influence with those of the ordinary Gyroscope, producing phenomena of which this instrument affords us the spectacle, a learned American has employed electricity as a motive power.
Fig. 277.—The Gyroscope.
The Gyroscope, shown in fig. 277, has a large, heavy pedestal, with a pointed column, which supports the instrument itself. The frame, of which the electro-magnets form a part, is connected with a rod, having at one end a hollow cavity which rests on the point of the vertical column. One of the extremities of the magnetic spool is attached to this cavity, the other end communicating with the bar which unites the two magnets. Over this bar is a spring which breaks the current, supported by an insulator in hard india-rubber; it is adjusted so that it touches a small cylinder on the axis of the wheel twice during every rotation of the latter. The wheel’s plane of rotation is at right angles with the magnets, and it carries an armature of soft iron, which rotates close to the magnet without touching it. The armature is so placed in relation to the surface of contact with the cylinder that breaks the current, that twice during each rotation, as the armature approaches the magnets, it is attracted; but immediately afterwards, as the armature comes directly in front of the magnets, the current is broken, and the acquired impulsion is sufficient to move the wheel until the armature comes again under the influence of the magnet. The spring which interrupts the current is connected with a thin copper wire, which stretches back as far as the point of the column, entwining it several times to render it flexible, finally bending down and plunging into some mercury enclosed in a round vulcanite cup placed on the column near the pedestal. The pedestal also bears two small stakes for receiving the wires of the battery, one connected with the column, and the other communicating by a small wire with the mercury contained in the vulcanite vessel. The magnets, the wheel, and all the connected parts can move in any direction round the point of the column. When two large Bunsen cells, or four small ones, are connected with the Gyroscope, the wheel turns with great rapidity, and allowing the magnets to operate, it not only sustains itself, but also the magnets and the other objects which are between it and the point of the column in opposition to the laws of gravitation. The wheel, besides turning rapidly round its axis, also effects a slow rotation round the column in the direction of the movement experienced by the lower part of the wheel. By placing the arm and the counterpoise of the machine as shown in fig. 277, so that the wheel and the magnets balance exactly on the pointed column, the whole machine rests stationary; but if we give the preponderance to the wheel and the magnets, the apparatus begins to rotate in a direction contrary to or following that of the upper part of the wheel.
The Gyroscope exemplifies very clearly the persistence with which a body undergoing a movement of rotation maintains itself in the plane of its rotation in spite of gravitation. It shows also the result of the combined action of two forces tending to produce rotations round two axes which are separate, but situated in the same plane. The rotation of the wheel round its axis, produced, in the present instance, by the electro-magnet, and the tendency of the wheel to fall or turn in a vertical plane, parallel to its axis, produce, as a result, the rotation of the entire instrument round a new axis which coincides with the column.
Peiffer’s Electrophorus.
It will now perhaps interest our readers to describe a charming little plaything which is a great favourite with children, and which has the incontestable merit of early initiating them into all the principal phenomena of the statics of electricity, and teaching them the science of physics in an amusing form.
It is a small electrophorus invented by M. J. Peiffer, and reduced to such a point of simplicity, that it consists merely of a thin plate of ebonite, about the size of a large sheet of letter paper. The tinned wooden disc of the electrophorus which is found described in most treatises on physics, is replaced by a small sheet of tin, about the size of a playing-card, fastened on to the surface of the ebonite. The ebonite electrophorus produces electricity with remarkable facility. It must be placed flat on a wooden table, and thoroughly rubbed with the hand; if it is then lifted, and the sheet of tin lightly touched, a spark is elicited from ¼ inch to ½ inch in length. The electrophorus is completed by the addition of a number of small accessories in the shape of small dolls made of elder-wood, which exhibit in a very amusing manner the phenomena of attraction and repulsion. After the board has been charged with electricity, place the three little figures on the sheet of tin, and lift up the apparatus, so as to isolate it from any support. You will then see one little doll extending its arms, another with its silky hair standing on end, and a third, lighter than the others, leaping like a clown, and displacing as he does so the two small balls of elder-wood which have been placed on each side of him. We have given an illustration of the three figures performing at once (fig. 278), but they are generally used separately. M. Peiffer has indeed collected every known accessory for an electric machine, such as Geissler’s tube, the electric carillon, etc. These different experiments are all reduced to their simplest form, and, with their appliances, are all contained in a cardboard box. They are placed beside the electrophorus, which thus takes the place of an unwieldy electric machine. M. J. Peiffer accompanies this little portable cabinet with an exhaustive pamphlet, which is a valuable guide to the young physicist in studying the first principles of electricity.
Fig. 278.—M. J. Peiffer’s electrophorus with dolls.