My position is perfectly definite. Gravitation, motion, heat, light, electricity and chemical action are one and the same object in various forms of manifestation.

Nature has put itself the problem how to catch in flight light streaming to the earth and to store the most elusive of all powers in rigid form. To achieve this aim, it has covered the crust of earth with organisms which in their life processes absorb the light of the sun and use this power to produce a continuously accumulating chemical difference. ... The plants take in one form of power, light; and produce another power, chemical difference.

The blood corpuscles take up the atmospheric oxygen in the lungs, and the vital chemical process accordingly depends essentially on the combination of oxygen absorbed by blood corpuscles with the combustible constituents of the blood to form carbonic acid and water.

The fall of a given weight from a height of around 365 meters corresponds to the heating of an equal weight of water from 0° to 1°.

The physiological combustion theory takes as its starting point the fundamental principle that the amount of heat that arises from the combustion of a given substance is an invariable quantity–i.e., one independent of the circumstances accompanying the combustion–from which it is more specifically concluded that the chemical effect of the combustible materials undergoes no quantitative change even as a result of the vital process, or that the living organism, with all its mysteries and marvels, is not capable of generating heat out of nothing.

Truly I say to you, a single number has more genuine and permanent value than an expensive library full of hypotheses.

In the firmament of science Mayer and Joule constitute a double star, the light of each being in a certain sense complementary to that of the other.

Ohm (a distinguished mathematician, be it noted) brought into order a host of puzzling facts connecting electromotive force and electric current in conductors, which all previous electricians had only succeeded in loosely binding together qualitatively under some rather vague statements. Even as late as 20 years ago, “quantity” and “tension” were much used by men who did not fully appreciate Ohm's law. (Is it not rather remarkable that some of Germany's best men of genius should have been, perhaps, unfairly treated? Ohm; Mayer; Reis; even von Helmholtz has mentioned the difficulty he had in getting recognised. But perhaps it is the same all the world over.)

Specialists never contribute anything to their specialty; Helmholtz wasn’t an eye-specialist, but a German army doctor who invented the ophthalmoscope one Saturday afternoon when there wasn’t anything else to do. Incidentally, he rewrote whole chapters of physics, so that the physicists only know him as one of their own. Robert Mayer wasn’t a physicist, but another country doctor; and Pasteur, who made bacteriology, was a tanner’s son or a chemist, as you will.