1880.] 



On an Electro- Magnetic Gyroscope. 



309 



Perhaps tlie best forms of the moveable piece are the spiral and 

 the copper disk, surrounded by a continuous ribbon of iron. 



No result was obtained with unmagnetisable substances, but the 

 experiments were not made with a sufficient degree of accuracy to 

 be deemed final. 



No attempt has been made either to ascertain whether the rotation of 

 the moveable pieces obtained by a motive power can produce alternate 

 currents in the coil, which appears to be very dubious, as the motion 

 is produced by the destruction of the symmetry which exists generally 

 between the two sides of a galvanometric frame. 



It can be very easily proved that the frame is an excellent magneti- 

 sing machine, and that the magnetisation takes place in the position of 

 equilibrium of a magnetised needle under a continuous current. If a 

 needle is placed horizontally within the frame, the end which is sent 

 forward becomes magnetic, so that it is very easy to alter the mag- 

 netism in any way which might be required. 



The induction machine which is presented has been reproduced 

 from one which M. Lontin had constructed for some special purposes, 

 described in a letter inserted in " Electricite" " (5th April last), and 

 the peculiarity of which is that inducing and induced wires have 

 a similar resistance. But I understand that the resistance of the wire 

 going round the frame may be enlarged to four times its present value 

 without diminishing the velocity of the rotation in any sensible manner. 

 So the actual conditions can be largely altered without interfering 

 with the production of the phenomena under consideration ; and it 

 may be inferred that the motive power derived from them can be 

 greatly increased by these obvious alterations, although it is quite 

 impossible to state whether it can be made useful to any practical 

 purposes. 



In concluding this short preliminary notice, I would venture to add 

 that the apparatus most nearly resembling mine is Faraday's disk, 

 with this difference, that it is made of mica and worked by a frictional 

 electrical machine. The mechanical work produced is very small in 

 either instrument. 



It may be stated to the credit of the gyroscope that the work done 

 by a man in turning the glass disk, is executed under the actual con- 

 dition by one Bunsen element of 20 centims. high ; so that in certain 

 respects the action may be said to be wonderfully great. But it must 

 not be forgotten that it is really Faraday's disk which has paved the 

 way in this new field of electrical researches ; and that certainly I 

 should not have taken advantage of the experiment shown to me by 

 M. Lontin, if I had not been acquainted with all the circumstances of 

 the disk rotation exhibited to me by your great natural philosopher so 

 many years ago. 



