202 Prof. E. Edlund on the 



vity moreover increases as the density of the gas diminishes. 

 The fact that gases heated to redness become conductors was 

 at first questioned, although erroneously, by Beetz * and G. 

 Wiedemann"! - , but has since been confirmed in the most com- 

 plete manner by Hittorf %. 



But Becquerel's experiment has furnished another result, 

 to which I will call special attention. When, keeping the same 

 battery, the intensity of the current was modified by introdu- 

 cing a rheostat of greater or less resistance, the resistance of 

 the gas was shown to be dependent on the intensity of the 

 current. For example, i and i x designating the current-inten- 

 sities, let E be the electromotive force, r and r x the resist- 

 ances of the solid or liquid conductor, z and Z\ the gas resist- 

 ances, corresponding to i and i l} we get, according to Ohm's 



E E 



formula, i= and ii= . When the current does not 



; r + z r x +z x 



pass through the gas, and M and M x designate the resistances 



necessary in order that the current-intensities may become the 



E E 



same as before, we shall have 4=^ and i x = ^-, whence we 



get M — r — z and M l —r 1 =z 1 . Putting the calculation thus, 

 it will be seen that the resistance of the gas was nearly pro- 

 portional inversely to the intensity of the current which had 

 passed. 



The observation numbers obtained also appear to indicate 

 that the resistance of the gas increases with the number of the 

 elements of the battery employed, although the intensity of the 

 current be maintained constant by introducing a suitable rheo- 

 static resistance. We will not now dwell upon this almost 

 incomprehensible result (as Becquerel himself remarks), seeing 

 that W. De La Eue and H. W. Miiller§ have quite recently 

 found, in their investigations, which, however, were executed 

 by other processes than those of Becquerel, that the resist- 

 ance of gases at one and the same current-intensity is inde- 

 pendent of the number of the elements. 



The above-mentioned differences between solid and liquid 

 conductors, on the one hand, and gases on the other, are ex- 

 plained without difficulty if the unitarian theory of the nature 

 of electricity explained by me|| be taken as the starting-point. 

 In order, however, to furnish the proof of what I advance, it 

 is necessary first to cite some propositions of that theory. 



* Fortsehrittt der Phi/si?;, ix. p. 479 (1863). 

 t Die Lehrevom Gahamsmus, 2nd ed. vol. i. p. 339. 

 X Pogg. Ann. Jubelland, p. 234 (1874). 

 § Phil. Trans, clxix. p. 230 (1878). 



|| Theorie des Phenomenes Elcctriques, Mem. Roy. Ac. Sciences, Sweden, 

 vol. xii. no. 8 (1874). 



