346 §=R. W. Willson—Demagnetization of Electro-magnets, 
du sang et en mesurer la force electromotrice. C. R., lvii, 791- 
95.) 
It is well known that muscular contractions can alter the 
character of the blood ; and we have shown that a very slight 
chemical difference between two fluids separated by a mem- 
brane of the same nature as the cutaneous covering of the 
fingers, will be shown by the galvanometer. 
IL—Demagnetization of Electro-magnets ; by Rospert W. WILL 
son, Junior Class, Harv. Coll. 
Wiedemann has shown Pogg. Ann. C. 235, Ann. de Min. 
(3), 1, 189, that the intensity of the current necessary to de 
magnetize a steel magnet is much less than that of the current 
by which the bar was originally magnetized. 
t has occurred to me to experiment, with a view to ascel 
taining how far this principle can be applied to electro-magnets 
The apparatus used consisted of a cylindrical bar of soft iron 
8 cm. in length and 1 cm. in diameter, slightly rounded at 
the end. The armature was a piece of soft iron, of the same 
diameter and 2 c.m. in length. ; 
round this core were placed two concentric helices, wound 
in opposite directions, through each of which could be passed 
the current of a single Grove’s cell. 
The method of experimenting was as follows. A current 
was first passed through the inner helix, which, for convement 
I shall call A, and the weight supported by the bar was no's 
This current being broken, the outer helix, B, was introd : 
into the circuit, and the corresponding weight noted. nee 
rent through B being then broken, and that through A cl si | 
after a short time, the current was again passed through B 
the weight noted. The following table shows the results. 
Wt. supported by— sane 
fe Pil is ‘a diminished by 5 
490 grms. 250 130 
470 240 130 
460 230 130 
460 220 120 
420 220 130 
410 200 110 
Mean 452 227 125 
Taking the mean result, we see that while the helix rat 
only develop sufficient magnetism in the bar to render 7 eer 
of sustaining 227 gr., yet, if it act in opposition "oT ers 
diminish the weight which the latter supports by 
that is, its power to demagnetize is greater than its 
magnetize, 
