1867.J Physics. 439 



temperature ; that when the gases are sufficiently rarefied for the 

 discharge to pass readily, and for the light to be stratified, this 

 elevation of temperature is less near the negative electrode than it is 

 near the positive electrode ; and that the absolute rise of temperature 

 at the two electrodes, and the differences between them, vary with 

 the density and nature of the gas. A fact which strikingly proves 

 the great calorific and illuminating power of electricity is that 

 hydrogen, under a pressure of only 1^ millim., may be rendered 

 luminous, and become sensibly heated by the passage of electricity, 

 although at this pressure its density is so small that a cubic centim. 

 of the gas weighs scarcely more than 5^ of a milligramme. The 

 gas must in fact have been very considerably heated for it to have 

 been able to raise the temperature of a thermometer, of which the 

 bulb filled with mercury was a cylinder 2J millims. in diameter 

 and 3 centims. long, 3° in two minutes. The simple fact that the 

 gas becomes luminous is a further proof of its high temperature ; 

 for its luminosity is evidently only a result of its incandescence. 

 Professor De la Eive concludes his long and interesting paper by 

 saying that * when one sees that so subtile a substance as hydrogen 

 reduced to 1 or 2 milhms. pressure is capable of becoming luminous 

 under the influence of electricity, it is impossible not to be tempted 

 to make a comparison between it and the likewise exceedingly 

 subtile but still luminous matter which composes the nebulse and 

 cometary bodies. This analogy becomes still more striking when 

 we examine closely the appearance presented, in a tube containing 

 rarefied hydrogen traversed by the electric discharge, by the kind of 

 mist which shows itself when a small quantity of gas is caused to 

 enter the tube, and which likewise appears in the dark space when 

 a certain degree of rarefaction has been passed. The gaseous 

 matter is there even more highly rarefied than it is at the other 

 parts of the mass, thus making its resemblance to the luminous 

 matter forming the comets and nebulae still more decided. We 

 may add that recent researches on the part of various astronomers 

 have shown that the rays yielded by the prismatic analyses of the 

 light of these celestial bodies are exactly similar to those given by 

 the electric discharge, when transmitted through rarefied nitrogen, and 

 especially through hydrogen. Do these gases, then, which intervene 

 in most of the phenomena of terrestrial physics, play an equally or 

 even more important part in the phenomena of cosmical physics ? 

 There is nothing improbable in this conjecture, especially since the 

 analysis of aerolites has shown that planetary space does not 

 contain any element not found also upon our globe. 



A curious experiment on the transportation of substances by 

 the voltaic and induction current has been published by M. Lewis 



* 'Phil. Mag.,' xxxiii. 260. 



