424 Mr. Faraday's Researches in Electricity. [Series XL) 



described in his beautiful and important investigations con- 

 tained in the Philosophical Transactions*; namely that induc- 

 tion is the same in rare and dense air, and that the divergence 

 of an electrometer under such variations of the air continues 

 the same, provided no electricity pass away from it. The 

 effect is one entirely independent of that power which dense 

 air has of causing a higher charge to be retained upon the 

 surface of conductors in it than can be retained by the same 

 conductors in rare air; a point I propose considering hereafter. 



1288. I then compared hot and cold air together, by raising 

 the temperature of one of the inductive apparatus as high as 

 it could be without injury, and then dividing charges between 

 it and the other apparatus containing cold air. The temper- 

 atui'es were about 50° and 200°. Still the power or capacity 

 appeared to be unchanged ; and when I endeavoured to vary 

 the experiment, by charging a cold apparatus and then 

 warming it by a spirit-lamp, 1 could obtain no proof that the 

 inductive capacity underwent any alteration. 



1289. I compared damp and dry air together, but could 

 find no difference in the results. 



1290. Gases. — A very long series of experiments was then 

 undertaken for the purpose of comparing different gases one 

 with another. They were all found to insulate well, except 

 such as acted on the shell-lac of the supporting stem ; these 

 were chlorine, ammonia, and muriatic acid. They were all 

 dried by appropriate means before being introduced into the 

 apparatus. It would have been sufficient to have compared 

 each with air ; but, in consequence of the striking result which 

 came out, namely, that all had the same power of, or capacity 



for, sustaining induction through them, (which perhaps might 

 have been expected after it was found that no variation of 

 density or pressure produced any effect,) I was induced to 

 compare them, experimentally, two and two in various ways, 

 that no difference might escape me, and that the sameness of 

 result might stand in full opposition to the contrast of pro- 

 perty, composition, and condition which the gases themselves 

 presented. 



1291. The experiments were made upon the following pairs 

 of gases. 



1. Nitrogen and Oxygen. 



2. Oxygen Air. 



3. Hydrogen Air. 



4. Muriatic acid gas Air. 



* Philosophical Transactions, 1834, pp. 223, 224, 237, 244. [See L. and 

 E. Phil. Mag. vol. iv. p. 436.— Edit.] 



