404 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Defection of the Magnetic Needle hy the act of Volition, 

 (taken from Phil. Mag, xxxiv, 543.) — This curious and interesting 

 experiment is due to the investigations of M. Du Bois Rcymond of 

 Berlin, and his method of performing it is as follows: — He takes a 

 very sensitive galvanometer, and attaches to the terminal wires thereof 

 two perfectly homogeneous strips of 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 

 alwavs observable a more or less decided deflection of the needle, this 

 deflection not being amenable to any known law, and being in the opin- 

 ion of the experimenter due fo the difference existing to some extent 



and in some way or another between the cutaneous covering of the two 

 fingers. Whenever there is a wound on one of the fingers the deflec- 

 tion 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 effects 

 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 constant 

 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 arms must be so braced that an equilibrium 

 may be established between the flexors and the extensors of all the 

 articulations of the limb, pretty much as in a gymnastic school is usu- 

 ally done when it is desired to exhibit the development of one's 

 muscles. 



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

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

 arm "an inverse current," according to NobilPs 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. Dubois Reymond himself 

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

 however movements in the needle of far greater extent bv contracting 

 alternately the muscles, first of one arm and then of the other, in time 

 with the oscillations of the needle. On bracing simultaneously the 

 muscles of both arms, inconsiderable deviations are observable, some- 

 times in one direction, sometimes in another; and these minute deflec- 

 tions are evidently attributable to the difference between the contractile 

 force of the two limbs. Hence it arises that when the experiment is 





