SPECIFIC INDUCTIVE CAPACITY OF GASES — ^ALIKE. 35 



the charge was found to be 29° ; then letting in air till the pressure was 30 inches, 

 the charge was still 29°. 



1286. Theseexperimentswere repeated with pure oxygen with the same consequences. 



1287. This result of no variation in the electric tension being produced by varia- 

 tion in the density or pressure of the air, agrees perfectly with those obtained by 

 Mr. Harris*, and described in his beautiful and important investigations contained in 

 the Philosophical Transactions ; namely that induction is the same in rare and dense 

 air, and that the divergence of an electrometer under such variations of the air con- 

 tinues 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 con- 

 ductors 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 temperatures 

 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 pur- 

 pose of comparing different gases one w^ith 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, ov capacity for, sustaining induction through them, (which per- 

 haps 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 property, composition, and 

 condition which the gases themselves presented. 



1291. The experiments were made upon the following pairs of gases. 



* Philosophical Transactions, 1834, pp. 223, 224, 237. 244. 



f2 



