34 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XI.) 



sible loss from the conducting power of app. i. ; and app. ii. were left charged to a 

 degree of tension above half the original charge, it would indicate that oil of turpen- 

 tine had less specific inductive capacity than air ; or, if left charged below that mean 

 state of tension, it would imply that the fluid had the greater inductive capacity. In 

 an experiment of this kind, app. ii. gave as its charge 390° before division with app. i., 

 and 175° afterwards, which is less than the half of 390°. Again, being at 175° before 

 division, it was 79° after, which is also less than half the divided charge. Being at 79°? 

 it was a third time divided, and then fell to 36°, less than the half of 79°. Such are 

 the best results I could obtain ; they are not inconsistent with the belief that oil of 

 turpentine has a greater specific capacity than air, but they do not prove the fact, 

 since the disappearance of more than half the charge may be due to the conducting 

 power merely of the fluid. 



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 constituted, and are bound together by so many striking physical and 

 chemical relations, that I expected some remarkable results from them : air in various 

 states was selected for the first experiments. 



1284. Ah\ rare and dense. — Some experiments of division (1208.) seemed to show 

 that dense and rare air were alike in the property under examination. A simple 

 and better process 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 circumstances 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, (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 re- 

 duced them still lower, that I might rarefy further, and for this purpose in the fol- 

 lowing 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, 



