and Olimic Resistance of Gases, 367 



to this case. If the reaction is supposed to take place iso- 

 therinally at a very high temperature, it is manifest that the 

 progress of the reaction from right to left must increase as 

 the concentration of the hydrogen — in other words, the ten- 

 sion of gas — is diminished. This we find to be the case : 

 the resistance of the gas increases, and the purity of the 

 " four-line " spectrum diminishes as the tension of the gas 

 increases, except when the gas is exceedingly rarefied. In 

 this case it is probable that the number of atoms present, 

 even if all were free, would be insufficient to carry all the 

 current. Hence we should expect to find this minimum at a 

 lower pressure when the capacity of the condenser employed 

 was less ; but, unfortunately, the spark is too uncertain at 

 these very low tensions, even with 20,000 volts from the 

 complete battery, to give definite results. 



Since hydrogen undoubtedly requires a very large amount 

 of heat for its dissociation, it follows that when the tempera- 

 ture is raised while the pressure is kept constant, more atoms 

 should be set free. We find, as a matter of fact, that the 

 resistance diminishes as we increase the capacity of the 

 condenser — that is to say, the heat of the discharge. The 

 case is exactly analogous to the dissociation of nitric peroxide 

 observed by E. and L. Natanson *. 



Our work leads one to infer that since a very high tempera- 

 ture is needed to produce the " four-line " spectrum of 

 hydrogen, this high temperature must be present whenever 

 this spectrum appears, for example, in the solar prominences 

 and in many fixed stars. The higher the tension of the gas, 

 the higher the temperature required ; hence one must know 

 the atmospheric pressures in these heavenly bodies before 

 attempting to guess at the actual temperature attained ; but 

 there can be no doubt that this temperature is in any case 

 far beyond the reach of any earthly means except the electric 

 discharge which we have been considering. 



Harvard University, Feb. 23rd, 1897. 



* Wied. Ann. xxiv. p. 454, and xxvii. p. 606. 



2F2 



