[From the Philosophical Magazine, for May, 1868.] 



XXXV. "Experiment in Magneto- Electric Induction." 

 IN A LETTER TO W. R. GROVE, F.R.S.* 



8, PALACE GARDENS TERRACE, W. 

 March 27, 1868. 



DEAR SIR, 



Since our conversation yesterday on your experiment on magneto- 

 electric inductionf, I have considered it mathematically, and now send you the 

 result. I have left out of the question the secondary coil, as the peculiar effect 

 you observed depends essentially on the strength of the current in the primary 

 coil, and the secondary sparks merely indicate a strong alternating primary 

 current. The phenomenon depends on the magneto-electric machine, the electro- 

 magnet, and the condenser. 



The machine produces in the primary wire an alternating electromagnetic 

 force, which we may compare to a mechanical force alternately pushing and 

 pulling at a body. 



The resistance of the primary wire we may compare to the effect of a 

 viscous fluid in which the body is made to move backwards and forwards. 



The electromagnetic coil, on account of its self-induction, resists the starting 

 and stopping of the current, just as the mass of a large boat resists the efforts 

 of a man trying to move it backwards and forwards. 



The condenser resists the accumulation of electricity on its surface, just as 

 a railway-buffer resists the motion of a carriage towards a fixed obstacle. 



* Communicated by Mr W. R. Grove, F.R.S. 

 t See Phil. Mag. S. 4. March 1868, p. 184. 



VOL. II. 16 



