and Ohmic Resistance of Gases. 363 



One of the great difficulties of investigating the inter- 

 mediate part of the curve lies in the fact that no tube is 

 strong enough to stand the continuous application of tempsra- 

 tures as high as those developed by the corresponding 

 current. On the other hand, the repeated, instantaneous 

 discharge, which the tube will stand, cannot be estimated 

 when the resistance rises above the very small amount 

 necessary to damp out the oscillations. 



The question whether the change in the spectrum, upon 

 increasing the current, is due to greater heat or to the oscil- 

 latory motion, is one which is not easily settled, because the 

 last trace of the return oscillation requires hundreds of ohms 

 for its damping ; and under these conditions this oscillation 

 is not easily photographed. The fact that argon offers no 

 less resistance than hydrogen or nitrogen to electric oscillations, 

 but nevertheless is much more sensitive to increased current, 

 tends to show that the important factor in the question is not 

 the oscillatory nature of the discharge, but only the great 

 quantity which is always attendant upon oscillatory discharges. 



Since gases do not strictly follow Ohm's law, we cannot 



assume that the formula R= i/i_^ in which R = resistance, 



L = self-induction, and C = capacity, and which gives the 

 limiting value of R for non-oscillatory discharges, rigidly 

 holds. If, however, we obtain a white glow in hydro o-en 

 which is due to the unidirectional discharge of a large con- 

 denser through a large resistance besides that of the tube, 

 and then proceed to increase the electromotive force, and 

 consequently the strength of the current in our unidirectional 

 discharge, we can determine whether this form of discharge 

 is competent to produce the red glow in hydro o-en. 



The apparatus which was used for this purpose consisted of a 

 step-up transformer consisting of two secondaries of many 

 turns of fine wire, which were slipped upon a long primary. 

 When the secondaries were coupled in series the electromotive 

 force of the discharge was doubled without any considerable 

 change in capacity. As a matter of fact the glosv was seen 

 to be perceptibly redder with two coils than with one, showing 

 that the change in the quantity is the essential feature in the 

 change of the spectrum. 



While this conclusion interferes with the strict application 

 of the word talantoscope to an argon -tube, the use of the tube 

 as a talantoscope nevertheless remains; for while the oscilla- 

 tions and the blue spectrum are not strictly dependent upon 

 one another they are both dependent upon the same final cause. 



