on various Phenomena of Induction, 273 



into the second, the direction of the two currents being the 

 same. Thus we find, that if the two inductor currents are 

 equal, the rheometric deviations which measure the intensities 

 are double what they are with a single current; and if the 

 currents are unequal, the deviations are the sum of the effects 

 of each elementary current (v). 



23. Second case. — I even employed the great helix and a 

 pile often pairs. The two inductor wires were joined end to 

 end, so that the direction of the current in the one was op- 

 posed to the direction of that in the other. The equality of 

 their dimensions and of their conductibility involved the 

 equality of the current which traversed each of them, a cur- 

 rent the value of which amounted to half that of the pile. The 

 induced currents also were perfectly equal, and as their direc- 

 tions were opposed, the needle of the rheometer remained 

 quite motionless. The result was the same whether the cir- 

 cuit was broken or closed (x). 



S*. That the indications of the rheometer are indeed the 

 measure of the currents simultaneously induced might be dis- 

 puted. In order to reply to this objection, I substituted the 

 metallic thermometer of Breguet for this instrument. At the 

 rupture as well as at the closing of the inductor currents, the 

 needle of this very delicate apparatus remained stationary. 

 This experiment repeated a great number of times invariably 

 gave the same result*. I also substituted the small helix for 

 the thermometer; small needles of tempered steel were not 

 magnetized, in its interior, either at the closing, or at the 

 rupture of the inductor currents. 



25. Third case. — This was examined by help of the great 

 helix, of two piles of ten pairs and of different wires. I was 

 led to the following conclusions : — 



a. When the length of one of the inductor wires remains 

 invariable, and that of the other is gradually increased, for the 

 lengths of the additional wire increasing in geometrical pro- 

 gression, the intensities of the induced current measured by 

 the rheometer diminish according to an arithmetical progres- 

 sion, the first term of which corresponds to the sum of the 

 effects of the inductor wires when the length of the additional 

 wire is null, and the last term of which is equivalent to the 

 action of the constant inductor wire taken by itself, whether 



* This experiment is interesting by its connexion with the researches of 

 Prof. Dove on the induced currents, which, equal in rheometricai measure, 

 produce at the same time very different physiological actions. See Bc- 

 richte der Berliner Akademie der Wissenschaften, 1839, p. 163. Archives de 

 I'Electricite, vol. ii. p. 290. 



Phil. Mag. S. 3. Vol. 25. No. 166. Oct. 1844. T 



