Principles of the Science of Motion. A7 
lines of pressure is evidently the resistance or non-displacement 
of the centres of one or more of the limiting atoms in the direc- 
tion of displacement, the more equally and quickly displacement 
of one atomic centre causes displacement of all neighbouring 
centres, the less will be the amplitude attained by the originally 
displaced molecule. 
15. The fitness of the conceptions here offered of the nature 
and states of electricity will appear chiefly in the proof of the 
generalizations to which they lead of the effects of electricity. 
But the above view of the nature of electricity is also founded 
on such facts as these. The “sources de l’électricité*,”’? mecha- 
nical, thermal, or chemical, are all motions, or conditions of 
displacement. These motions are of different momenta. Com- 
pare facts as to the heterogeneousness of the bodies in frictional 
and thermal electricity ; and as to their compound character in 
chemical electricity, interpreted by the theory of the chemical 
constitution of bodies hereinafter enunciated. In reference to 
the above conception of the difference of electricities, compare 
facts proving “‘ the identity of electricities derived from different 
sources},” and, more particularly as to intensity, the various facts 
defining the correlative conceptions of insulation and discharge. 
16. (IL.) The states of electricity are thus conceived. (1) In 
a statically electrified body, the tension, or displacement of the 
molecular centres of pressure, is in closed curves forming the 
surface of the body, and the direction of displacement is either 
outwards (positive) or inwards (negative) ; and it seems demon- 
strable that there will be such a displacement only on the surface 
of the body. 
“17. Compare such facts as :—it is the least resisting of two 
rubbed bodies that is found negatively electrified ; if an elec- 
trified sphere is hollow, there will be little or no electricity on the 
inner surface, &c. 
18 Two conditions have been well distinguished by Ampéref 
in (2) dynamically electrified bodies—that of “ courant ouvert,” 
and that of “courant fermé.’”’ The former is conceived as a con- 
dition of longitudinal, the latter of transverse or spiral tension. 
Hence a polarity corresponding to the duality of statically 
electrified bodies. For electric poles are conceived as extremi- 
ties towards, and from, which molecular centres of lines of pres- 
sure have been moved, at which, therefore, there is not only a 
change in the mechanical relations to outward atoms of the lines 
of pressure from these extremities, but a change at the one ex- 
‘tremity of increase, at the other of diminution, of pressure. And 
* De la Rive, Traité de l Electricité, cinquiéme partie, 1. 456—828, 
ft Faraday, ‘ Experimental Researches,’ Series IV. 
t Ampére, Théorie des Phénoménes Electrodynamiques, Paris, 1826. 
