of Electricity through Rarefied Air. 3 



current in the opposite direction to the principal current. It 

 will be experimentally proved, further on, that this is indeed 

 the case, and that, at least when the rarefaction has reached a 

 certain limit, this force undergoes continuous augmentation if 

 the rarefaction be carried still further. But it will be conve- 

 nient, before passing to the statement of the experiments per- 

 formed, to call attention to the following circumstances : — 



I have demonstrated, in my unitary theory of electricity, 

 that the resistance undergone by an electric current in passing 

 through a solid or liquid conductor will be proportional to the 

 intensity of the current*. As I have shown in that memoir, 

 the supposition hitherto regarded as true, that the resistance 

 is independent of the intensity of the current, really leads to 

 absurd conclusions; while the supposition that the resistance 

 of the conductor is proportional to the intensity of the current 

 is found to be in complete conformity with the experiments 

 hitherto made, and leads to results ratified by experience. 

 What has just been said applies to solid and liquid bodies, but 

 not to gases at ordinary temperature, as the following consi- 

 deration, among others, w r ill show: — In order that a current 

 started by an electromotor may be able to pass through a solid 

 or liquid conductor, there is no need of a determined electro- 

 motive force in the electromotor. However slight the force 

 may be, the current will always pass, although of course it 

 becomes less intense in proportion as the electromotive force 

 is little or the resistance of the conductor is great. If in all 

 cases the current is able to traverse the conductor, that evi- 

 dently depends on the effective resistance being proportional 

 to the intensity of the current, and hence that resistance is 

 least when the intensity of the current is least. On the con- 

 trary, in order that the current may be able to pass through a 

 gaseous body, a determined electromotive force is necessary, 

 or, what amounts to the same, it is necessary that the electro- 

 motor be in a condition to produce a certain tension on the 

 electrodes. If the electromotive force is below this limit, 

 experiment shows that gas may be regarded as a perfect insu- 

 lator. From this it evidently follows that the resistance of 

 gases cannot be proportional to the intensity of the current. 

 Now, if it be admitted that the electric resistance of gases is 

 independent of the intensity of the current, the properties of 

 which, according to the experiments of the last few years |> 



* "Th^orie des c phenomenes electriques," K. Svenska Vet.-Akad. 

 Handlingar, t. xii. no. 8 ; Pogg. Ann. cxlviii. p. 421 (1873); Phil. Mag. [4] 

 xlvi. p. 204. 



\ Bihang till K. Svenska Vet.-Akad, Handlingar, vi. no. 7 (1881) : 

 Wied. Ann. xv. p. 165 (1882) ; Phil. Mag. [5] xiii. p. 200. 



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