668 



withdrawn. No sooner was the current discontinued than the mus- 

 cles were affected with spasmodic contractions, and with a tetanoid 

 rigidity, constituting the secondary, or what the author denominates 

 the electrogenic condition ; an effect, which as instantly subsides on 

 the restoration of the voltaic current. 



The author proceeds to state the precautions which must be taken 

 to ensure the success of experiments on this subject; and traces the 

 effects of desiccation of the nerves from spontaneous evaporation, 

 and of the ajoplication of external moisture, on the phenomena ; and 

 also the modifications introduced by varying the extent of voltaic 

 contact. Various experiments are then described, which the author 

 instituted with a view to ascertain the nature of the electrogenic 

 condition of the nerves, and the circumstances under which it is in- 

 duced ; and he is led to the conclusion that the phenomena involve 

 some voltaic principle which has not hitherto been fully investigated. 



March 11, 184-7. 



The MARQUIS OF NORTHAMPTON, President, in the Chair. 



" On the cause of the discrepancies observed by Mr, Baily v/ith 

 the Cavendish Apparatus for determining the Mean Density of the 

 Earth." By George Whitehurst Hearn, Esq., of the Royal Mili- 

 tary College, Sandhurst. Communicated by Sir John F. W. Her- 

 schel, Bart., F.R.S. 



After taking a summary review of the methods employed by Mr. 

 Baily for determining, on the plan devised by Mr. Cavendish, the 

 mean density of the earth, and of the anomalies, hitherto unac- 

 counted for, which. had introduced perplexity in the results obtained, 

 the author, suspecting that these anomalies had their source in the 

 variable magnetic states of the masses which w^ere the subject of 

 experiment, traces the effects which such an influence might be 

 supposed to have on those results. He finds that, the attraction 

 arising from gravitation between a mass and one of the balls being 

 exceedingly minute, an almost inconceivably feeble magnetic state 

 may be the cause of great perturbations. He then proceeds to in- 

 vestigate the subject by the application of mathematical analysis ; 

 from which he is led to the conclusion that the masses and balls do 

 actually exert on one another influences which are independent of 

 the action of gravitation. He finds that such influences are of a 

 very fluctuating nature ; the action arising from them being either 

 positive or negative, and its sign also changing in each revolution 

 as the masses are turned round a vertical axis ; and he observes that 

 such action may either fall short of that arising from gravitation or 

 exceed it many times. Such disturbing force he conceives can be no 

 other than a magnetic influence ; not however one of the ordinary 

 kind, but that which Faraday has recently discovered as affecting 

 all diamagnetic bodies. 



