54>4i Intelligence and Miscellaneous Articles. 



platina. These strips are dipped down into two vessels filled with 

 salt and water, into which fluid, as contained in each vessel, two 

 corresponding fingers of the two hands are to be plunged. On the 

 first immersion of the fingers there is almost always observable a 

 more or less decided deflection of the needle, this deflection not being 

 amenable to any known law, and being in the opinion of the experi- 

 menter due to the diflference existing to some extent and in some 

 way or another between the cutaneous covering of the two fingers. 

 Whenever there is a Avound on one of the fingers the deflection is 

 greater than usual ; and its direction is uniformly such that the injured 

 finger behaves like the zinc- side of an arc of zinc and copper, which 

 we may conceive to be inserted between the two vessels instead of 

 the human body. It need hardly be remarked, that it is not this sort 

 of action to which in the experiment in question it is purposed to 

 direct the attention. On the contrary, in order to observe the eff^ects 

 alluded to, it is requisite to wait either till the needle has gone back 

 to the zero-point of its scale, or at least until it has assumed a con- 

 stant deflection attributable to the residue of a current which it is 

 beyond us to eliminate. As soon as this state is attained, the whole 

 of the muscles of one of the arras must be so braced that an equili- 

 brium may be established between the flexors and the extensors of 

 all the articulations of the limb, pretty much as in a gymnastic school 

 is usually done when one wants to let a person feel the development 

 of one's muscles. 



As soon as this is done the needle is thrown into movement, its 

 deflection being uniformly in such a sense as to indicate in the braced 

 arm " an inverse current," according to Nobili's nomenclature ; that 

 is to say, a current passing from the hand to the shoulder. The 

 braced arm then acts the part of the copper in the compound arc of 

 zinc and copper mentioned above. 



With his own galvanometer, and when M. Du Bois Reymond him- 

 self performs the experiment, the deflection amounts to 30°. He 

 obtains however movements in the needle of far greater extent by 

 contracting alternately the muscles, first of one arm and then of the 

 other, in time with the oscillations of the needle. On bracing simul- 

 taneously the muscles of both arms, inconsiderable deviations are 

 observable, sometimes in one direction, sometimes in another ; and 

 these minute deflections are evidently attributable to the diflfer- 

 ence between the contractile force of the two limbs. Hence it arises 

 that when the experiment is repeated many times in succession, the 

 results diminish gradually in amount, not only in consequence of the 

 energy of the contractions becoming less and less, but also because 

 it becomes more and more difficult to restrain the act of slackening 

 or letting down the muscles to only one of the two arms. 



The amount of deviation, cateris 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 

 respect. There are indeed individuals who do not possess the power 

 of producing a sensible deflection in the jieedle of his galvanometer. 



