LECTURE VI.
THE CORRELATION OF THE PHYSICAL FORCES.
We have frequently seen, during the course of these lectures, that one of those powers or forces of matter, of which I have written the names on that board, has produced results which are due to the action of some other force. Thus, you have seen the force of electricity acting in other ways than in attracting: you have also seen it combine matters together, or disunite them, by means of its action on the chemical force; and in this case, therefore, you have an instance in which these two powers are related. But we have other and deeper relations than these; we have not merely to see how it is that one power affects another—how the force of heat affects chemical affinity, and so forth—but we must try and comprehend what relation they bear to each other, and how these powers may be changed one into the
