and its Effects. 135 



Mixed Cases. 



By mixed cases I understand those wherein a branched com- 

 munication exists between the poles of the induction wire, and 

 where each branch presents one of the before-mentioned cases. 

 We have just considered a combination of the second and third 

 cases, wherein one branch was interrupted by air, and the other 

 contained an insulating body. A combination of the first and 

 third does not appear to promise much interest ; consequently 

 with two branches only, we have but to consider the combination 

 of the first and second cases. 



When cc is an unbroken metallic circuit, and instead of 

 the jar a well-exhausted egg is introduced at ab, no light ap- 

 pears in the latter as long as the wire presents a less resist- 

 ance. If the resistance be increased, however, either by using 

 a longer or a thinner wire, the current divides itself between 

 both circuits, and the egg becomes luminous. In general 

 this division evidently takes place according to the same laws 

 which hold for the galvanic current, and doubtless if the resist- 

 ances in the primary and branch circuits, as well as the electro- 

 motive force of the induction were known, the intensity of the 

 induction current in both branches could be expressed by the 

 same or similar formulae to those used in galvanism. The phse- 

 nomena are here more complicated, merely because the induction 

 apparatus furnishes two alternating currents of opposite direc- 

 tions, of which one has not the power of passing through the 

 egg. Through the primary circuit Pc or Nc both currents pass 

 alternately and with equal intensity ; through ca, be the current 

 at breaking contact alone passes; and again, through cc both 

 currents pass, but with unequal intensities, for the current at 

 closing is greater than the current at breaking contact, because 

 a part of the latter has ])assed along ca, be. Hence, when the 

 galvanometer is introduced into Pc or Nc, no deviation (or an 

 ambiguous one when the current is sufficiently intense) is 

 obtained ; in cb or ca a deviation corresponding to the current 

 at breaking contact is found ; and in cc the deviation opposite 

 to this, corresponding to the current at making contact. These 

 phajnomena were very distinct when one of the 10,000-feet 

 wires was employed to generate the induction current, and the 

 other to make the branch cc. They were also evident, though 

 accompanied with far less light in the egg, when cc consisted of 

 the wire 1200 feet long and 25 millim. thick. 



Miscellaneous Phanomena. 

 Many very instructive experiments can be made with two or 

 more instruments, of which the following may be mentioned. 

 The induction current can be excited in one apparatus and 



