to account for the Vhcsnomena of Electricity . 349 



fiositive electricity is not an accumulation, nor negative a defi- 

 ciency of this peculiar matter : that jars in order to become 

 charged, need not assume the characters of the two states : and 

 that when discharged the electrical appearances do not cease. 



5. Tiie filth and last position relates to the excitation of 

 electrics. Franklin's supposition is, that " glass, a body ex- 

 tremely elastic, must ^^•hen rubbed have its rubbed surface some- 

 what stretched, or its solid parts drawn a little further asunder, 

 ^o that the vacancies in which the electric iiuid resides, become 

 larger, aftbrding room for more of that fluid, wliich is imme- 

 diately attracted into it from the cushion or hand rubbing, they 

 being supplied from the common stock. Eut the instant tha 

 parts so opened and filled, have passed the friction, they close 

 again, and force the additional quantity out on the surface""." 



This statement appears very objectionable. Granting that 

 glass when rubbefl may have the interstices between its particles 

 enlarged, why should electricity rush into them ? If any do en- 

 ter it must be at the expense of the rubber. But the rubber it- 

 self has'^a strong attraction to its natural quantity; it sliould be 

 left negative, and the glass would be positive ; therefore, as there 

 is so strong an attraction between such states, the equilibrium 

 would be instantly restored. There is not even any reason why 

 the equilibrium should have been disturbed : the repulsion is on 

 every side equal, and Franklin allows that under such circum- 

 «tances, there can be no disturbance. If the pores of the glass 

 be opened, it does not follow that they should have u tendency 

 to take in more electricity. There are much more efficient 

 modes of increasing the distance of the particles, for instance by 

 heating, and yet this is an operation seldom connected with 

 electrical appearances. 



Frankhn supposes that no electricity can 1)e received upon 

 one surface of glass unless the other can part with an equal 

 quantity. In the case of the excitation of tlie common cylinder, 

 the inner surface having no connection with conductors can part 

 with none : how then can its outer surface receive the great 

 <iuantities that we find on it ? 



In the excitation of an clectrophorus, the vacancies by rul)- 

 bing may be enlarged: but when the rubjjing ceases, they should 

 close and expel all electricity. So contrary is this to fact, that by 

 one excitation seven or eight hundred sparks may be obtained. 

 But what is still more irreconcilable is that while the sulphur 

 cake and metallic plate are in contact, if the latter be gently 

 passed off akmg the surface of the sulphur^ scarcely another 

 spark can be obtained. 



■* jTankliii,78. 



It 



