PEIFFER'S ELECTROPHORUS. 279 



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 

 lay 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 incon- 

 testable 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 \ inch to \ 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 



