IQQ ELECTRICL EFFECTS PRODUCED BV FRICTION. ^ 



*' another, a number of points in the surface of the rubber are 

 " first brought into contact with a corresponding set of points 

 " in the surface of the IocIt/ rubbed ; that they are then sepa- 

 " rated from themj and brought lalo contact wkh another set of 

 " points J and so on, until the one body has passed entirely over 

 " the other. Now, at each separation, if the bodies be of different 

 " kinds, whether conductors or nonconductors, the general 

 " law, we have stated, must operate, and opposite electrical 

 " states must be excited in the separated particles. So far, 

 " therefore, the excitement by friction, and the excitement by 

 " contact and separation, appear to be referrible, in a general 

 " manner, to the same principle. We shall now proceed to a 

 '^ more particular consideration of the subject." 

 diffictk'to^^ 3. To this consideration I shall soon come ; but I must firsr' 

 prove. observe, that it would be very difficult to prove that theory by 



ascertaining the eflfects of the friction in diflferent points of the 

 rwWer and the body rubbed, in order to find out their j&ro^rew. 

 We see, upon the whole, that one is become negative, when 

 the other is made positive ; but nothing can indicate whether 

 these effects are produced during the contact, or only at the 

 separation. Therefore the decision of this point must pro- 

 ceed from other phenomena, and Dr. Maycock affords me an 

 opportunity of discussing this point by the passage which fol- 

 lows that above quoted. 

 Principal facts " The principal facts (he says) relative to the excitement of 

 dtement^°bv ^ " ^^^^^^ hy friction, may be expressed by the five following 

 friction, ac- ''propositions. 1. To produce excitement by friction, it 

 hi'ra""^*^'^ " is essentially necessary that one of the bodies employed in 

 "the operation be of the class of electrics. 1. If two electrics, 

 " or arj electric and an insulated conductor be employed, the one 

 " body will, after the operation, indicate an electricity opposite 

 " to that which is indicated by the other. 3. The effect of 

 *' friction performed with one combination of dissimilar bo- 

 " dies is different from that which is produced by any other 

 "combination, 4. The /ric/io?: of two bodies, similar in all 

 " respects to one another, produces no excitement. 5. If the 

 " rubier of an electrical machine be insulated, only a very 

 " slight charge can be accumulated in the prime conductor j 

 " and, under such circumstances, the action of the machine 

 *' soon ceases altogether." 



5. I 



