1880.] Induction of Electric Currents in Infinite Plates, fyc. 113 



hands of my friend and colleague, Professor Roscoe, F.R.S., the only 

 sample available of the protagon of which the analyses had been 

 communicated to the Royal Society ; this was a twice re- crystallized 

 sample of protagon from ox-brain, which had been employed for 

 analyses 3 and 4. The remaining specimens had been used in experi- 

 ments on the products of decomposition of protagon. 



I requested Dr. Roscoe, to whom I communicated Dr. Thudichum's 

 criticism, to determine the amount of mineral impurities, and 

 especially of potassium present in protagon. He has kindly fur- 

 nished me with the ensuing report, with which I shall close this com- 

 munication, as I am convinced that no one will expect me to enter 

 into a polemical discussion with the author of the previously quoted 

 matter. 



The Owens College, Manchester, 



December, 1879. 



I have examined spectroscopically for potash a sample of protagon 

 furnished me by Dr. Gamgee, and labelled " Protagon twice re- 

 crystallized. Blankenhorn." I could not detect any potash by the 

 spectroscope in the incinerated mass from O'l grm. of substance. With 

 the carbonized mass obtained from 1*0 grm. of substance 1 obtained 

 the potassium line (a) very faintly, and from comparative experi- 

 ments with a dilute solution of a potassium salt, I estimate the 

 quantity of potash in 1 grm. of the substance not to exceed -^V mgrm. 

 The carbonized residue of 1 grm. of protagon was carefully oxidized 

 with pure nitric acid, when a small quantity of fused metaphosphoric 

 acid remained after ignition. This residue weighed 0*0278 grm., 

 corresponding to T08 per cent, of phosphorus.* 



(Signed) H. E. Roscoe. 



III. " On the Induction of Electric Currents in Infinite Plates 

 and Spherical Shells." By C. NiVEN, M.A., Professor of 

 Mathematics in Queen's College, Cork. Communicated by 

 J. W. L. Glaisher, M.A., F.R.S. Received January 21, 

 1880. 



(Abstract.) 



The object of the present paper is to determine the currents which 

 are induced in an infinite plate of uniform conductivity and finite 

 thickness, and in a sphere or spherical shell of any thickness when in 

 the presence of a varying magnetic system : and in any of these 

 bodies when rotating near a constant magnetic system, round an axis 

 which is normal to the faces of the plate or passes through the centre 



* The mean quantity of phosphorus found by Gramgee and Blankenhorn was 

 1-068 per cent. — A. a. 



VOL. XXX. I 



