Specific Inductive Capacity of Air, 423 



1282. Naphtha. — This liquid gave results similar in their 

 nature and direction to those with oil of turpentine. 



1283. A most interesting class of substances, in relation to 

 specific inductive capacity, now came under review, namely, 

 the gases or aeriform bodies. These are so peculiarly con- 

 stituted, and are bound together by so many striking physical 

 and chemical relations, that I expected some remarkable re- 

 sults from them : air in various states was selected for the first 

 experiments. 



1284. Air, rare and dense, — Some experiments of division 

 (120S.) seemed to show that dense and rare air were alike in 

 the property under examination. A simple and better pro- 

 cess was to attach one' of the apparatus to an air-pump, to 

 charge it, and then examine the tension of the charge when 

 the air within was more or less rarefied. Under these circum- 

 stances it was found, that commencing with a certain charge, 

 that charge did not change in its tension or force as the air 

 was rarefied, until the rarefaction was such that discharge 

 across the space o, o (fig. 1.) occurred. This discharge was 

 proportionate to the rarefaction; but having taken place, 

 and lowered the tension to a certain degree, that degree was 

 not at all affected by restoring the pressure and density of 

 the air to their first quantities. 



Inches of Mercury. 



Thus at a pressure of 30 the charge was 88° 



Again 30 the charge was 88 



Again 30 the charge was 87 



Reduced to 14 the charge was 87 



Raised again to 30 the charge was 86 



Being now reduced to 3*4 the charge fell to 81 



Raised again to 30 the charge was still 81 



1285. The charges were low in these experiments, first 

 that they might not pass off at low pressure, and next that 

 little loss by dissipation might occur. I now reduced them 

 still lower, that I might rarefy further, and for this purpose 

 in the following experiment used a measuring interval in the 

 electrometer of only 15° (1185.). The pressure of air within 

 the apparatus being reduced to 1*9 inches of mercury, the 

 charge was found to be 29^ ; then letting in air till the press- 

 ure was 30 inches, the charge still 29°. 



1286. These experiments were repeated with pure oxygen 

 with the same consequences. 



1287. This result of no variation in the electric tension 

 being produced by variation in the density or pressure of the 

 air, agrees perfectly with those obtained by Mr. Harris, and 



