Royal Society. 73 



himself to the subject of the electrogenic condition of the muscular 

 nerves, postponing to future inquiries that of the incident nerves 

 and of the spinal marrow ; and also the modes of action of other 

 physical and chemical agents, such as mechanical injury, heat and 

 cold, strychnine, and the hydrocyanic acid. 



The bones and muscles of the brachial lumbar and pelvic regions 

 of a frog, being isolated from all the other parts of the body, except- 

 ing only by means of their respective brachial and lumbar nerves, 

 which were perfectly denuded on all sides, and raised from the glass 

 on which the limbs were laid, a voltaic current from a pair of the 

 " couronne de tasses" was passed downwards through the nerves, in 

 a direction from their origin in the spinal marrow towards their ter- 

 minations in the muscles. Energetic muscular movements were at 

 first excited ; and the current was thus continued during the space 

 of five, ten, or fifteen minutes, and at the end of this period was 

 withdrawn.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 6f the application 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 II. — "On the cause of the discrepancies observed by 

 Mr. Baily with the Cavendish Apparatus for determining the Mean 

 Density of the Earth." By George Whitehurst Hearn, Esq., of the 

 Royal Military College, Sandhurst. Communicated by Sir John 

 F. W. Herschel, 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 jierplexity in the results obtained, 

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

 variable magnetic states of the masses which were 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 



