The whole aim of the science is to state the phenomena of nature in terms of these quantities in the most exact language possible. From this point of view, a notable distinction in the kindred science of chemistry is at once apparent in that whereas chemistry introduces no new entity, it subdivides matter into upwards of eighty distinct ultimates called elements, thus enormously enlarging the number of combinations and phenomena with which it must deal.
Biology, again, while retaining all the postulates of physics and chemistry, introduces a new principle, that of life, whereby the phenomena to be treated become infinitely complex.
If we now recall that it is only the simplest phenomena of nature that can be formulated, it is at once obvious why chemistry and biology are so much more backward in their growth into exact sciences, the former being largely taken up with a description of the properties of different substances, while the latter can do little more than group together different living forms according to some principle of resemblance amid diversity. These differences make it evident that the character of mind best adapted for their investigation may differ somewhat in the different sciences, and also that the effects when taught will be more or less diverse. Different methods of presentation may likewise be found desirable.
In physics three modes of teaching are available, each of which is to be employed in conjunction with the others, each contributing an indispensable, but necessarily different and unequal, portion to the learner. They are (1) recitations upon a text-book, (2) demonstration of phenomena in lectures, (3) work in a physical laboratory. Now while there is nothing in these methods peculiar to the teaching of physics, it is important to observe that not only do the function and service of each method differ considerably in any one science, but that both the function and service of any method are widely different in different sciences. The function of the text-book is chiefly historical, i. e., to record what progress in the development of the science has been effected by our predecessors; but in connection with physics it can not be too strongly emphasized that the science is not a bare record of observations upon natural phenomena. There is nothing more characteristic of the mental attitude of the physicist toward knowledge than the constant desire to answer not alone the question 'how?' but 'how much?' That is to say in other words, we begin to have adequate knowledge of a fact only when we can measure it.
A musician will say without hesitation that one composition is more classical than another. The insufficient and essentially subjective character of such knowledge is at once apparent if we press the question 'when is one composition twice as classical as another?'
Physics is not a bare record of facts, but a highly developed system
