I<5i2 PHENOMENA ACCOMPANYING 



ures of 1 to 10"»"», even whcu the absolute temperatures, witli which they must 

 uot be coufbunJed, vary with the pressure aud with the nature of tlie gases. 

 Thus, even when there is uo longer any sensible obscure space at the negative 

 electrode, the thermometer is less elevated there than in the neighborhood of 

 the positive, which })roves that the gas is there more dilated and of more con- 

 ducting capacity** The difference of temperature, then, should be a still more 

 sensible criterion than the difference of brightness, of the greater or less electric 

 resistance of different parts of the gaseous column. The absolute temperature 

 is iu general less in hydrogen at all degrees of rarefaction than in nitrogen and 

 atmospheric air, which offer more resistance to the passage of electricity. The 

 difference between the two thermometers was, moreover, never so great in hydro- 

 gen as in nitrogen, or atmospheric air. Thus it was at the maximum of 4^°* 

 in hijdrogcn, under the pressure of 9 to 12™™, the thermometer having risen, 

 in two minutes, from 21"^ to 2G^" at the negative electrode, and 21° to 31° at 

 the positive, in nitrogen the maximum difference was 5° under the pressure 

 of 5™™, (20° to 24° at the negative thermometer, 20° to 29° at the positive.) 

 In atmospheric air the maximum difference was, at a pressure of 6™™, 6°, (from 

 18° to 2G° at the negative thermometer, and from 18° to 32° at tlie positive.) 

 At a pressure of 20™™ the difference was not more in hydrogen than 2.}°, (from 

 21° to 28^°, and from 21° to 26°;) in nitrogen but a half degree, (from 20° to 

 to 25°, and from 25° to 25^°;) and in atmospheric air it was null, (from 19° to 

 28° at the two thermometers alike.) When there is no longer a difference be- 

 tween the indications of the two thermometers, or that difference is very slight, 

 it will be observed that the appearance of the luminous stream is perfectly 

 uniform through its whole extent. 



llere we give a table of some experiments : 



ATMOSPHKKic AIR, (duration of the experiment, two ininutes.) 

 Pressure. Positive tliermometer. Negative thermometer. Difference. 



2™™ 16° to 25° 16° to 21° 4° 



4™™ 18° to 31° 18° to 25^° 5.^° 



6™™ 18° to 32° 18° to 26° 6° 



8™™... 18° to 31° 18° to 27i° 3|° 



10™™ 18° to 31° 18° to 28° 3° 



15™™.^ 18J° to 31° 18^° to 29° 2° 



20™™ 19° to 28" 19° to 28° 0° 



NITROGEN, {duration of the experiment, tioo minutes.) 



2™™ 19° to 24° 19° to 22° 2° 



4™™ 20J° to 28° 20J° to 25° 3° 



5™™ 20° to 29° 20° to 24° 5° 



6™™ 20° to 31^° 20° to 27° 4.^° ■ 



9™™ 20° to 31° 20° to 27° 4° 



15™™ 21° to 30° 21° to 27° 3° 



20™™ 20° to 25i° 20° to 25° ^° 



IIYUROGEN, {duration of the cxpcrivient, two minutes.) 



2«»» 21° to 27" 21° to 25° 2° 



5™™ 20° to 28^° 20° to 25i° 3° 



G™™ 21° to 29° 20° to 25i° 3^° 



9™™ 21° to 31° 20° to 26|° 4|° 



15™™ 21° to 30° 21° to 26° 4° 



2p™™ 21° to 28^° 21° to 26° 2^° 



30™™ 21° to 25° 21° to 23 J° l|° 



* The thermometric indications are in degrees of Keaumiur. 



