362 Messrs. Trowbridge and Richards on the Temperature 



the condenser discharge, according to Hittorf ' s results already 

 quoted. 



It is clear that the quantity of electricity going through the 

 tube in a given time is almost incredibly different in the two 

 cases. This difference has not been enough emphasized in 

 the literature upon the subject. Suppose that the battery 

 and other resistance are so regulated as to supply a milli- 

 ampere of current, and the condenser is of such a size that 

 when it is connected the spark passes ten times a second. 

 These conditions were frequently those of our experiments. 

 The spark, judging from our photographs, certainly does not 

 last more than one millionth of a second, hence the current- 

 strength at the instant of the discharge must be at least 

 100,000 times as great as that of the continuous discharge 

 without the condenser, or must amount to 100 amperes. 



Jaumann's observation that the opposition to the current is 

 less as the current increases, and our conclusion (III.) that 

 the resistance is less with the larger capacity, are in reality 

 observations which may be represented as the two extremities 

 of a long curve. This curve is formed by the relation of 

 milliamperes to megohms on one end, and of hundreds of 

 amperes to ohms upon the other. The part of the curve 

 between these two extremities is very hard to investigate 

 with our present means, and indeed it seems to behave 

 differently with different gases. For these two conditions 

 are represented in any given case by the two spectra of the 

 gases, and as we increase the current we observe varying 

 relations between these spectra. In the case of hydrogen the 

 spectrum of four visible lines gradually increases in brilliancy 

 with the gradual fading of the many-lined spectrum of the 

 lower temperatures as the current is increased ; and only 

 when the current-strength becomes very great do the extra 

 lines disappear. In other words, the change from one 

 condition to the other is gradual. In the case of nitrogen, 

 upon the other hand, the change is abrupt : and often when 

 the gas is near its sensitive point some sparks will go through 

 with little opposition, while others give the banded spectrum 

 and the non-oscillatory photograph, showing that the resis- 

 tance was large. Argon is like nitrogen in the suddenness 

 of the transition, but its transition takes place with much 

 weaker currents than with either hydrogen or nitrogen. We 

 have repeatedly found argon to give the pure blue spectrum 

 under the influence of the discharge of the full battery with 

 very little resistance in the circuit without any condenser, or 

 with less than eight amperes ; for the resistance of each cell 

 of the battery is about the quarter of an ohm. 



