3 



experiments intended to prove the insulating property of the ma- 

 terials employed, the author goes on to observe that there is but one 

 way of explaining the phenomena in question, namely, by supposing 

 that the individual particles or molecules of the non-conducting 

 cylinder acquire different electrical states at their opposite extremi- 

 ties, and that these electrical states, while they are readily developed 

 and neutralized within each particle, meet with great resistance in 

 passing from one particle to another, a condition of non-conducting 

 bodies which constitutes the molecular electric polarization of 

 Faraday. 



The author then gives the result of some experiments on the 

 amount of electrical charge communicated to, or given out by an 

 insulated conducting ball surrounded, at one time by air, at another 

 time by an insulating substance, such as sulphur. 



In conclusion, the author thinks that the following propositions 

 may be regarded as rigorously demonstrated by experiment : 



1 . The effects produced on insulating cylinders in the presence 

 of an electrified body, depend on the state of molecular electric 

 polarity which that body developes in the cylinders ; and thus the 

 hypothesis of Faraday is directly demonstrated by experiment. 



2. Other circumstances being alike, the insulating power of a 

 substance is greater in proportion as its degree of polarization is 

 weaker. 



3. The electric capacity of a conducting body that is, the quan- 

 tity of electricity which it acquires when placed in communication 

 with a source of electricity is much greater when the body is 

 surrounded with sulphur, or some other solid isolating substance, 

 than when surrounded by air. Similarly, the body being electrified 

 from the same source and then surrounded with sulphur, or else 

 surrounded with air, afterwards yields to the same conductor much 

 less electricity in the former case than in the latter. 



4. The effects produced by insulating plates interposed between 

 the armatures of a Leyden jar or of a magic square are explained, 

 together with the phenomena previously described, both by the 

 penetration of the electricity into the interior of the insulating sub- 

 stance, and the propagation of electricity along the surface of the 

 plates. 



