692 Proceedings of Royal Society of Edinburgh. [sess. 
in the latter some are more, and some less, electrified, and it 
is the difference of action of these differently electrified bodies 
on the medium and of the medium on the bodies which causes 
all the phenomena of electricity. We have seen that when two 
different substances are rubbed and pressed together the one 
becomes positively and the other negatively electrified — that is 
to say, that the constituent particles of the positively electrified 
body have gained speed, and those of the negatively electrified 
body have lost an equal amount, through their contact with one 
another. By the increase of speed thus gained the atoms and 
molecules of the positively electrified body would become more 
separated from one another by their recovery from collapse , as 
though by an increase of heat, and this without a commensurate 
increase in their heat or state of vibration. They would thus 
electrify the space in which they moved more strongly, and 
without a commensurate increase in their heat vibrations, etc., to 
nullify the electrification. On the other hand, the atoms and 
molecules of the negatively electrified body, by the speed lost by 
their particles, would cling more closely together through their 
greater collapse ; in this state they would electrify their spaces less 
strongly through having practically the same heat and elastic 
absorption and less electricity. The one would gain electricity 
without a gain in heat, or elastic absorption, and the other would 
lose electricity without a loss of either of the others.* They 
would have the same space to electrify — the one with more 
electricity to do it with and the other with less to do it with. 
The state of equilibrium existing in the medium would be thus 
upset, the positive body energising it more, and the negative 
body energising it less, than the surrounding neutral bodies. 
* It is found that electrified bodies when heated lose their charges, but 
that negative electrification is more readily discharged than positive. This 
is in accordance with the present theory, for negative electrification is a 
lack of electricity which heat can readily supply — that is to say, that some 
of the latter becomes transformed into the former till the neutral state is 
reached. In the case of positive electricity the heated body would retain its 
charge for some time, till by the increase of the vibrations the whole of it 
would be transformed into heat. 
In flames a chemical change is going on where both positive and negative 
electricity are present and being converted by their great affinity for one 
another into heat. 
