Chemistry and Physics. 405 



repeated many times in succession, the results diminish gradually in 

 amount, not only in consequence of the energy of the contractions be- 

 coming less and less, but also because it becomes more and more diffi- 

 cult to restrain the act of slackening or letting down the muscles to only 

 one of the two arms. 



The amount of deviation, cater is paribus, depends upon the amount 

 of the development and the exercise of the muscles. The author is 

 said to have an arm of considerable power, and among the number of 

 savans that have tried the experiment at his residence, there has not as 

 yet been found one who excelled or even came up to him in this re- 

 spect. There are indeed individuals who do not possess the power of 

 producing a sensible deflection in the needle of his galvanometer, but 

 it is readily ascertained that in these instances there is a want of suffi- 

 cient muscular tension. 



There is one remark, to conclude, which the author has been fre- 

 quently led to make, namely, that the habitual superiority of the right # 

 hand over the left in this experiment is to be interpreted by the pre- 

 ponderance of the amount of deflection produced by the tension of the 

 right arm. This peculiarity was likewise observed when the experi- 

 ment was performed by M. von Humboldt. The impulsion impressed 

 on the needle by the contraction of the muscles of his right arm was 

 appreciably more considerable than that produced by his left arm. 



For his own part, M. von Humboldt has addressed to M. Arago a 



i letter of the following tenor: — He says, the fact of the experiment of 



affecting a magnetic needle by the alternate tension of the muscles of 

 the two arms, an effect due to volition, is established beyond all ques- 

 tion or doubt. Notwithstanding my advanced years and the little 

 strength that I have in my arms, the deflections of the needle were 

 v ery considerable; but they were naturally more so when the experi- 

 ment was performed by M. J. Miiller or by M. Helmkoltz, who are 

 younger men. To facilitate the experiment it is advisable to plunge 

 the fore-fingers into the water, and to support the palms of the hands, 

 to enable one to brace up well the muscles of the arm which it is pur- 

 posed to bring into play. 



2. On the Development of Electricity in the Act of Muscular Con- 

 traction; by M. Becquerel, (Compt. Rend., May, 1849; Phil. Mag M 

 xxxv, 53.)— i have repeated unsuccessfully the experiment of M. Du 

 Bois Reymond, relative to the production of an electric current in the 

 act of muscular contraction, making use of the arrangements which he 

 indicated in a letter addressed to M. Arago by M. de Humboldt, dated 

 the 17th of May, excluding however, all those secondary causes which 

 could give rise to electric currents, excepting that one, the action of 

 which is described. 



i shall commence by recalling to mind the observations which 1 made 

 »n studying the electric effects obtained with a condenser, the plates of 

 which were made of platinum or copper gilt {Traite de VEleclncxte et 

 du Maonetisme, t. v. 2 e partie, page 10) :— ^ 



. " The electro-chemical effects produced on the contact of acid solu- 

 t'ons with the liquids which moisten the fingers, must be taken into ac- 

 count. I n these various reactions the acids acquire positive electri- 



Shcond Series, Vol. VIII, No. 24.— Nov., 1849. 



52 



