NATURAL PHILOSOPHY. 169 



If we remain faithful to the hypothesis of the fluids, the most simple way 

 to electrify a body would assuredly appear to be by taking the fluid where 

 it exists in a free state, and to communicate, to pour it out (if the expres- 

 sion may be allowed) as it were by a direct contact. This we see constantly 

 used, when we witness a conductor sustained by some insulating support, 

 placed in contact with an electrical machine previously charged : commonly 

 the operator has not the time to place them in contact, for before they 

 touch the spark leaps forward, and the division is made. And if the 

 operator pleases to employ some known methods of observation, it may 

 be seen that, during the period the two machines are being brought together, 

 a change takes place in the state of the conductor, which greatly precedes 

 the explosion of the spark. By the influence exerted within a certain 

 radius of distance by the supposed machine charged with positive elec- 

 tricity, the natural distribution of the fluids is troubled ; each of them, 

 has yielded to the disposition which characterizes it : the negative fluid 

 advancing towards the positive fluid which attracts it, and the positive 

 fluid of the bodies taking refuge in the parts of the surface farthest from 

 the machine. The result is, the different points of this surface are 

 iiiequally and differently electrified ; in the hypothesis of a complete 

 isolation, this state, which constitutes electrization by influence, would 

 persist for an indefinite period. If, on the contrary, the machine be 

 removed, or its charge be dissipated in the ground, the influence having 

 disappeared, the conductor would immediately return to its natural state. 

 Thus electrization by influence differs essentially from that which results 

 simply from the accumulation of one or the other fluid. Here the same 

 electricity is in the preponderance throughout the whole extension of 

 the surface of the bodies ; the tension is in every respect positive or 

 negative, as is exhibited by the usual experiments of the electroscopic 

 pendulum, and the plan tfepreuve, where neither the pendulum nor the 

 body can regain their natural state, except by losing its fluid in excess, or 

 by gaining the contrary fluid. There, on the contrary, electrization by 

 influence divides the surface of the body into two distinct regions one 

 of the positive tension, the other with the negative tension ; and these two 

 regions are separated by a neutral line where the tension is null. Besides, 

 the fluids thus localized in two distinct regions exist in proportions meet 

 for the reformation of the neutral fluid, so that the operator has but to 

 remove the acting cause to obtain this recomposition and to reconstitute 

 the body in its natural state. 



A clear distinction of the two phenomena is necessary to a perfect concep- 

 tion of the positions of Melloni. He commences his paper with recalling 

 sententiously, as suited with his learned audience, these facts as having 

 been definitively admitted in science, and as forming the foundation of the 

 theory of static electricity ; and then he announces that he has before 

 him. results from experiments which make a great breach in the funda- 

 mental theorem of electrization by influence. 



According to Melloni, the plan d'ejjreuve and the electroscopic pendu- 

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