VOL. LXVIII.] PHILOSOPHICAL TRANSACTIONS. 467 



glass or sealing wax. The only material difference between the conducting and 

 non conducting substances seems to be, that the electricity does not spread itself 

 so easily and so rapidly through or on those bodies which are non-conductors, as 

 on those which are conductors. An electrical spark thrown on the surface of a 

 piece of metal insulated, of whatever length it be, diffuses itself equally through 

 the whole mass, if this metal be left to itself out of the sphere of action of 

 another body charged with electricity. The whole electricity communicated by 

 this spark is discharged at once by touching any part of the same metal. On 

 the contrary, electricity seems rather to stick to that part of a non-conducting 

 body to which it is applied, spreading but slowly and unequally over its surface, 

 from which it may be taken by degrees, by touching those parts to which it was 

 applied. There are some bodies which seem to be of a middle state between 

 these two, viz. through which the electric fluid propagates as through good 

 conductors, but slowly, such as common wood, moist air, and many other 

 bodies. Electricity seems to diffuse itself through these bodies almost as sugar 

 and salt diffuse themselves through water, spreading farther and farther through 

 the liquid. 



8. All those bodies which are non-conductors seem to acquire a state of elec- 

 tricity with some reluctance ; and, after they have acquired it, to hold it more 

 tenaciously, or to part with it more reluctantly than conductors. One touch 

 takes away all the electricity of a metallic body, but does not absolutely convey 

 away all the electricity of a piece of glass or another electric body, such as seal- 

 ing wax, amber, &c. The metal plate of an electrophore takes hardly any elec- 

 tricity at all from the resinous cake, if it be lifted up without having been 

 touched when it was on the cake. 



g. All resinous bodies, silk and many others, retain more tenaciously their 

 state of electricity than glass, however dry. Thus a piece of glass excited is 

 almost quite deprived of its electricity by a conducting substance being applied to 

 it ; but a resinous body, though touched, retains slill a great share of its elec- 

 tricity. 10. A conducting body insulated, being placed within the sphere of 

 action of an excited non-conducting body, or even in contact with it, acquires 

 at the same time 1 contrary electricities ; viz. the part in contact, or very near 

 the non-conducting electrified body, acquires a contrary electricity to that of the 

 non-conducting body, at the same time that the opposite or farthermost extre- 

 mity is possessed of the same electricity with the non-conducting body. 11. A 

 conducting body insulated, being in contact with another conducting body ex- 

 cited with either electricity, acquires the same electricity throughout its whole 

 extension, or divides with this body its electricity equally. 12. But an insulated 

 conducting body, being only in the sphere of action of another electrified con- 

 ducting body, acquires, as in the first mentioned case, two different electricities 



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