210 
under the influence of heat, may be enormously expanded, as is 
seen to be the case with respect to the comm, of some comets on 
approaching the sun. At the surface of a liquid there is an excess 
of molecular attraction, giving rise to the phenomena of Capillary 
Attraction , but tire resulting action is too feeble to affect sensibly 
the fluidity. On the contrary, in the solid state each atom in the 
superficiafstratum is equilibrated by counteracting atomic repul- 
sions and molecular attractions in such manner that fluidity is 
destroyed and the atom can only oscillate about a certain normal 
position. Experience, however, shows that this state of the super- 
ficial stratum may be altered by friction applied at the surface, 
and that the atoms may thus be made to take other positions, which 
it is found, they retain with more or less persistence, till at length 
the substance returns to its normal condition. Whilst the super- 
ficial atoms are in the abnormal positions the substance is in an 
electrified state. _ 
(9.) It seems evident that when by friction the superficial atoms 
are disarranged and the electrified state is induced, forces are called 
into play which disturb the equable distribution of the atoms in 
the interior of the substance. They must become in some degree 
more closely packed at some parts than at others, anu there will 
consequently be a gradation of atomic density. Now I have 
succeeded in showing, on the before-mentioned hypotheses oi the 
hydrodynamical origin of attractive and repulsive forces, that so 
Iona- as by the action of such forces the substance is maintained in 
the constrained state above described, there will also be maintained 
steady ethereal streams circulating in, and in the neighbourhood 
of, the substance. The dynamical effects of these streams account 
for electrical attractions and repulsions. _ . 
(10.) Galvanic Force accords with Electric Force so far as both 
are due to the agency of ethereal streams which have their oiigin 
in disturbances of the atomic state of superficial strata. Lut in 
o-alvanism the disturbance is the result of contact of dissimilar 
'substances , intensified generally by the action of acids ; and because 
this generating process is of a continuous kind, it is necessary to 
provide conducting wires for the circulation of the streams, oi for 
transmitting them from one position to another in the earths 
interior. Whilst in these respects electricity and galvanism differ, 
the conditions of polarity are the same in both. 
(11.) In the generation, by Seebcck’s experiment, of thermo - 
qalvanic currents, the requisite gradation of interior atomic density 
'is produced by unequally heating the two ends of a lamina of 
met til 
(12.) There is nothing in the state of the superficial atoms of a 
magnet which has any relation to magnetic force. Yet this, like 
