A letter to Prof. Faraday. 5 



(See par, 1616.) Must not every particle be excited negatively, if 

 it be excited positively ? Must it not have a negative, as well as 

 a positive pole ? 



I cannot agree with you in the idea that consistently with the 

 theory which ascribes the phenomena of electricity to one fluid, 

 there can ever be an isolated existence either of the positive or 

 negative state. Agreeably to this theory, any excited space, 

 whether minus or plus, must have an adjoining space relatively 

 in a different state. Between the phenomena of positive and 

 negative excitement there will be no other distinction than that 

 arising from the direction in which the fluid will endeavor to 

 move. If the excited space be positive, it must strive to flow 

 outward ; if negative, it will strive to flow inward. When suffi- 

 ciently intense, the direction will be shown by the greater length 

 of the spark, when passing from a small ball to a large one. It is 

 always longer when the small ball is positive, and the large one 

 negative, than when their positions are reversed.* 



But for any current it is no less necessary that the pressure 

 should be on one side comparatively minus, than that on the 

 other side, it should be comparatively plus ; and this state of the 

 forces must exist whether the current originates from a hiatus 

 before, or from pressure behind. One current cannot differ essen- 

 tially from another, however they may be produced. 



In paragraph 1330, I have been struck with the following 

 query, " What then is to separate the principle of these extremes, 

 perfect conduction and perfect insulation, from each other ; since 

 the moment we leave the smallest degree of perfection at either 

 extremity, we involve the element of perfection at the opposite 

 ends ?" Might not this query be made with as much reason in 

 the case of motion and rest, between the extremes of which there 

 is an infinity of gradations ? If we are not to confound motion 

 with rest, because in proportion as the former is retarded, it differs 

 less from the latter ; wherefore should we confound insulation 

 with conduction, because in proportion as the one is less efiicient^ 

 it becomes less remote from the other ? 



In any case of the intermixture of opposite qualities, may it 

 not be said in the language which you employ " the moment we 



* See my Essay on the causes of the diversity in the length of the sparks, erro- 

 neously distinguished as positive and negative, in vol. v, American Philosophical 

 Transactions. 



