THE GYROSCOPE. 743 



projectiles to turn round very rapidly, their axis preserves an invariable 

 direction during their whole course, until they finally strike the object at 

 which they are aimed. Without this rotation they would pirouette in an 

 irregular manner in the air, and besides any precision in firing being impos- 

 sible, the resistance of the air would diminish their range to an enormous extent. 



The Gyroscope, an instrument now familiar to most scientific persons, 

 is still a problem of which the solution has not yet been found. It may be 

 called the paradox of mechanics, for although it depends on gravitation, it 

 appears to be entirely indifferent to it. 



An American scientist has applied electricity to the gyroscope, so as to 

 make its movements as continuous as possible, and to enable us to study it 

 more at leisure and with better results. The gyroscope is mounted on a 

 pedestal which tapers to a point, and supports the instrument. The bar of 

 the gyroscope on which the electro-magnets are fixed rests upon the top of 

 the pedestal. One of the extremities of the bobbin is fixed to the cavity, 

 when the bar and support join, the other extremity communicates with the 

 tar which joins the nuts of the magnets. 



An insulator of hardened caoutchouc is so placed that it just touches 

 the axis of the wheel twice in every revolution of that wheel. Its plane of 

 rotation is at right angles to the magnets, and carries an armature of soft 

 iron which turns very close to the magnet without touching it. The arma- 

 ture is put en rapport with the surface of contact of the cylinder, so that 

 when the armature approaches it is attracted ; but immediately afterwards, 

 as it reaches the opposite side, the current is interrupted, and the impulse 

 acquired is sufficient to move the wheel to the spot where the armature can 

 again come under the influence of the magnet. 



The magnets, the wheel, and all the parts of the instrument together 

 can move around in any direction. When two or four Bunsen cells are 

 put in connection with the gyroscope, the wheel turns with tremendous 

 rapidity, and by permitting the magnets to work (an operation which 

 requires some little dexterity), the wheel not only sustains itself, but also 

 the magnets and the other subjects which are between it and the extremity 

 of the pedestal in opposition to the laws of gravitation. The wheel, 

 besides turning rapidly around its axis, revolves slowly around the point of 

 the column in the same direction taken by the lower part of the wheel. 



When attaching the arms and counter-poise of the machine, so that 

 the wheel and the magnets may balance themselves exactly on the pointed 

 pedestal, the machine remains stationary. But if we give any preponderance 

 to the wheel and magnets the rotation of the apparatus is in a direction 

 opposite to that which would result from turning the upper part of the wheel. 



The gyroscope illustrates the persistence with which a body that 

 submits to rotation maintains itself in the plane of its rotation, notwithstand- 

 ing the force of gravitation. It also shows the result of the combined action 

 of two forces tending to produce rotation around two separate axes, which 

 are, however, situated in the same plane. 



