"We advise all men," says Bacon, "to think of the true ends of knowledge, and that they endeavor not after it for curiosity, contention, or the sake of despising others, nor yet for reputation or power or any other such inferior consideration, but solely for the occasions and uses of life." It is difficult to imagine any other basis upon which the study of physics can be justified than for the occasions and uses of life; in a certain broad sense, indeed, there is no other justification. But the great majority of men must needs be practical in the narrow sense, and physics, as the great majority of men study it, relates chiefly to the conditions which have been elaborated through the devices of industry as exemplified in our mills and factories, in our machinery of transportation, in optical and musical instruments, in the means for the supply of power, heat, light, and water for general and domestic use, and so on.
From this narrow practical point of view it may seem that there can be nothing very exacting in the study of the physical sciences; but what is physics? That is the question. One definition at least is to be repudiated; it is not "The science of masses, molecules and the ether." Bodies have mass and railways have length, and to speak of physics as the science of masses is as silly as to define railroading as the practice of lengths, and nothing as reasonable as this can be said in favor of the conception of physics as the science of molecules and the ether; it is the sickliest possible notion of physics, whereas the healthiest notion, even if a student does not wholly grasp it, is that physics is the science of the ways of taking hold of things and pushing them!
Bacon long ago listed in his quaint way the things which seemed to him most needful for the advancement of learning. Among other things he mentioned "A New Engine or a Help to the mind corresponding to Tools for the hand," and the most remarkable aspect of present-day physical science is that aspect in which it constitutes a realization of this New Engine of Bacon. We continually force upon the extremely meager data obtained directly through our senses, an interpretation which, in its complexity and penetration, would seem to be entirely incommensurate with the data themselves, and we exercise over physical things a kind of rational control which greatly transcends the native cunning of the hand. The possibility of this forced interpretation and of this rational control depends upon the use of two complexes: (a) A logical structure, that is to say, a body of mathematical and conceptual theory which is brought to bear upon the immediate materials of sense, and (b) a mechanical structure, that is to say, either (1) a carefully planned arrangement of apparatus, such as is always necessary in making physical measurements, or (2) a carefully planned order of operations, such as the successive operations of solution, reaction, precipitation, filtration, and weighing in chemistry.
These two complexes do indeed constitute a New Engine which helps the mind as tools help the hand; it is through the enrichment of the materials of sense by the operation of this New Engine that the elaborate interpretations of the physical sciences are made possible, and the study of elementary physics is intended to lead to the realization of this New Engine: (a) By the building up in the mind, of the logical structure of the physical sciences; (b) by training in the making of measurements and in the performance of ordered operations, and (c) by exercises in the application of these things to the actual phenomena of physics and chemistry at every step and all of the time with every possible variation.
That, surely, is a sufficiently exacting program; and the only alternative is to place the student under the instruction of Jules Verne where he need not trouble himself about foundations but may follow his teacher pleasantly on a care-free trip to the moon or with easy improvidence embark on a voyage of twenty-thousand leagues under the sea.
What it means to study physical science may be explained further by mentioning the chief difficulties encountered in the teaching of that subject. One difficulty is that the native sense of most men is woefully inadequate without stimulation and direction for supplying the sense material upon which the logical structure of the science is intended to operate. A second difficulty is that the human mind is so in the habit of considering the practical affairs of life that it can hardly be turned to that minute consideration of apparently insignificant details which is so necessary in the scientific analysis even of the most practical things. Everyone knows the capacity of the Indian for long continued and serious effort in his primitive mode of life, and yet it is difficult to persuade an Indian "farmer" to plow. Everyone knows also that the typical college student is not stupid, and yet it is difficult to persuade the young men of practical and business ideals in our colleges and technical schools to study the abstract elements of science. Indeed it is as difficult to get the average young man to hold abstract things in mind as to get a young Indian to plow, and for almost exactly the same reason. The scientific details of any problem are in themselves devoid of human value, and this quality of detachment is the most serious obstacle to young people in their study of the sciences.
A third difficulty which indeed runs through the entire front-of-progress of the human understanding is that the primitive mind-stuff of a young man must be rehabilitated in entirely new relations in fitting the young man for the conditions of modern life. Every science teacher knows how much coercion is required for so little of this rehabilitation; but the bare possibility of the process is a remarkable fact, and that it is possible to the extent of bringing a Newton or a Pasteur out of a hunting and fishing ancestry is indeed wonderful. Everyone is familiar with the life history of a butterfly, how it lives first as a caterpillar and then undergoes a complete transformation into a winged insect. It is, of course, evident that the bodily organs of a caterpillar are not at all suited to the needs of a butterfly, the very food (of those species which take food) being entirely different. As a matter of fact almost every portion of the bodily structure of the caterpillar is dissolved as it were, into a formless pulp at the beginning of the transformation, and the organization of a flying insect then grows out from a central nucleus very much as a chicken grows in the food-stuff of an egg. So it is in the development of a young man. In early childhood the individual, if he has been favored by fortune, exercises and develops more or less extensively the primitive instincts and modes of the race in a free outdoor life, and the result is so much mind-stuff to be dissolved and transformed with more or less coercion and under more or less constraint into an effective mind of the twentieth-century type.
A fourth difficulty is that the possibility of the rehabilitation of mind-stuff has grown up as a human faculty almost solely on the basis of language, and the essence of this rehabilitation lies in the formation of ideas; whereas a very large part of physical science is a correlation in mechanisms.
The best way of meeting this quadruply difficult situation in the teaching of elementary physics is to relate the teaching as much as possible to the immediately practical and intimate things of life, and to go in for suggestiveness as the only way to avoid a total inhibition of the sense that is born with a young man. Such a method is certainly calculated to limber up our theories and put them all at work, the pragmatic method, our friends the philosophers call it, a method which pretends to a conquering destiny.