"In early physical systems we have optics dealing with phenomena perceived by the eye; acoustics treating of auditory percepts, and so on. The subjective concepts of "tone" and "colour" have now been replaced by the objectified concepts of frequency of vibration; and wave-length. The object of this process of elimination is, according to Planck, the striving towards a unification of the whole theoretical system, so that it shall be equally significant for all intelligent beings."

“A great number of our common ideas and ways of looking at the world were really shaped for us by the Greeks of antiquity, and... incorporated into the scientific knowledge of today. Such ideas as those of matter, force, element, number, space, time, etc., came to us from the ancient Greeks.”

“An explanation of a phenomenon is regarded, apparently instinctively, as the most general possible when it is a mechanical explanation. The "mechanism" of the process is the ultimate goal of experiment. Now this mechanism in general lies beyond the range of the senses; either by reason of their limitations, as in the case of the atomic structure of matter, or by the very nature of the supposed mechanism, as in the theory of the ether. The only way to bridge the gap between the machinery of the physical process and the world of sense-impressions is to think out some consequence of that mechanism. This we will call the hypothesis. The hypothesis, resting still on the mechanical basis, is yet beyond the range of direct experimental investigation; but if, by mathematical reasoning, a consequence of the hypothesis can be deduced, this will often lie within the range of experimental inquiry, and thus a test of the soundness of the original mechanical conception may be instituted.”

“As an instance of the remarkably far-reaching effect which a single mathematico-physical concept has had upon the development of chemical theory, one has but to recall the state of chemistry just before the revival of Avogadro's law by Cannizzaro, to be impressed by its confusion. Relying solely upon their "chemical instinct," the leaders of the various schools of chemical thought had developed each his own theoretical system. ...a host of ...conceptions strove for supremacy. The strife was stilled, order and unity were restored, as soon as Avogadro's great idea was seen in its true light, and the concept of the molecule was introduced into chemistry. A formula which had required pages of reasoning from a purely chemical standpoint to establish, and that insecurely, was fixed by a single numerical result.”

“We perceive clearly that theories and hypotheses are not accepted or rejected outright; they have their periods of activity, and then lie dormant for a time, only to be revived in a new form later on.”

“Higher Mathematics for Chemical Students”

“The fundamental materials from which we construct our picture of the universe may appear in different shapes, but there is really very little discontinuity between what seem at first sight very different views.”