A letter to Prof. Faraday. an , & 
(See par. 1616.) Must not every particle be excited inedavely, 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 .. plus; and this state of the 
forces must exist whether the current originates from a 2 hinting 
before, or from pressure behind. One current cannot differ essé 
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 
oe the latter; wherefore should we confound insulation 
with conduction, because in proportion as the one is less eee, 
it becomes less remote from the other? 
In any case of the intermixture of opposite Be may it 
not be said in the language which you employ “the moment we 
my Essay on the causes of the div ersity in the length of the sparks, erro- 
’ : owl; distinguished as positive and negative, in vol. v, American Philosophical 
- ‘Fransaetions. 
