On the Electric Properties of Insulating Bodies. 533 



following, as one of a peculiar and unstudied class. If in the series 

 1, 3, 5, 7, &c. four terms be taken, and the next one omitted, then 

 the four next terms taken and the next three omitted, then four 

 terms taken and^re omitted, and so on, the four terms taken will 

 in every case consist of numbers prime to one another. 



" On the Electric Properties of Insulating or Non-conducting 

 Bodies." By Professor Carlo Matteucci of Pisa. 



The object of the author in the first part of this memoir is to 

 ascertain by experiment what condition is assumed by insulating or 

 non-conducting bodies in the presence of an electrified body, and in 

 what degree such condition is developed in insulating bodies of 

 different kinds. In a memoir published nearly ten years ago (Ann. 

 de Chim. et de Phys., xxvii. p. 134), he had shown that a cylinder of 

 gum-lac, sulphur, stearic acid, or the like, suspended by a filament 

 of silk, and brought near to a body charged with electricity, begins 

 to oscillate in the same way as a cylinder of metal. The non-con- 

 ducting cylinder, whilst under the influence of induction, behaves 

 like any body charged with opposite electricities, and returns to its 

 natural state when the induction ceases. 



These experiments have now been very carefully repeated with 

 cylinders formed of vaiious insulating substances, made as nearly as 

 possible of the same length and perfectly diselectrized. The air was 

 rendered perfectly dry, and the inducing ball was charged with 

 electricity to a constant degree, measured by the torsion-balance. 



After giving a numerical statement of the time of oscillation and 

 the moment of the induced force, as determined by experiment for 

 cylinders of different insulating substances, and after describing other 

 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 Ijody, depend on the state of molecular electric 

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

 hypothesis of Faradaj' 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. 



