48 Dr. Hare's Letter to Prof. Faraday 



requires that there shall be in any body possessing it, two 

 opposite poles. Hence you correctly allege that agreeably 

 to your views it is impossible to charge a portion of matter 

 with one electric force without the other. (See par. 1177.) 

 But if all this be true, how can there be a " positively excited 

 particle?" (See par. 1616.) Must not every particle be ex- 

 cited negatively, if it be excited positively? Must it not have a 

 negative, as well as a positive pole? 



14>. 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 endeavour to move. If the excited space be posi- 

 tive, it must strive to flow outward; if negative, it will strive 

 to flow inward. When sufficiently 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 *. 



15. 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 ori- 

 ginates from a hiatus before, or from pressure behind. One 

 current cannot differ essentially from another, however they 

 may be produced. 



16. In paragraph 1330, 1 have been struck with the follow- 

 ino 1 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 per- 

 fection at either extremity, we involve the element of perfec- 

 tion 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 propor- 

 tion as the former is retarded, it differs less from the latter; 

 wherefore should we confound insulation with conduction, be- 

 cause in proportion as the one is less efficient, it becomes less 

 remote from the other ? 



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

 erroneously distinguished as positive and negative, in vol. v. American 

 Philosophical Transactions, 



