300 Prof. F. Gotch and Mr. G. J. Burch. Electrical 



dimensions of the atoms are concerned in the matter, for the inter- 

 space in the centre of a primitive cube of potassium is large enough 

 to house an atom of a gross volume exceeding 17. 



In the case of iron the central space is notably smaller than in 

 that of palladium ; supposing no expansion to occur on absorption, 

 the largest atom it could contain would have a diameter of 1/392, 

 corresponding to a volume of 2*697. 



It is probable, however, that a change in crystalline system is 

 associated with the absorption of gases by iron and nickel. This 

 is suggested by the curious effect produced on the nature of these 

 metals by repeated absorption of hydrogen, at least in the case of 

 nickel, which loses its cohesion and after repeated treatment becomes 

 converted into a friable powder. 



The galleries formed by ranges of central spaces present con- 

 strictions at intervals corresponding to the places where the four 

 spheres forming the face of a cubelet are most closely approxi- 

 mate; the ratio of the diameter of a sphere that could just traverse 

 one of these constrictions is to that of a sphere which would jnsfc 

 occupy a central space as v/2 : -v/3. Hence the passage of an atom 

 into the central chamber involves either a displacement of the atoms 

 surrounding the entrance or a contraction in the volume of the 

 entering guest. Is it possible that the " singing " of palladium, 

 which accompanies the process of occlusion, is connected with vibra- 

 tory movements of its atoms as they open and close the entrances to 

 the central chambers ? 



In conclusion it may be pointed out that all the metals which are 

 known to occlude hydrogen, viz., potassium, sodium, magnesium, 

 iron, nickel, platinum, and palladium, are paramagnetic, sodium and 

 magnesium being the only cases of an uncertain nature, while lead 

 and gold, which offer roomy central spaces for the occupation of 

 hydrogen, but do not absorb it, are diamagnetic. 



u The Electrical Response of Nerve to a Single Stimulus 

 investigated with the Capillary Electrometer. Pre- 

 liminary Communication." By F. GOTCH, M.A., F.R.S., 

 Professor of Physiology, University of Oxford, and G. J. 

 BURGH, M.A. (Oxon). Received April 1, Read May 12, 

 1898. 



The electrical changes which are evoked in nerve by a single 

 stimulus have up to the present been but little investigated. The 

 examination of the phenomena has been almost entirely limited to 

 observations upon the gal vanome trie deflections caused by the summed 

 effects of a rapid succession of excitations, and rheotome methods, 



