Popular Science Monthly/Volume 15/June 1879/The Study of Physics in the Secondary Schools
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The Study of Physics in the Secondary Schools
By John Townsend Trowbridge
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ASSISTANT PROFESSOR OF PHYSICS IN HARVARD UNIVERSITY.
PHYSICS is a comprehensive term for the laws of the physical universe, and is gradually superseding the old term natural philosophy which held together in a disconnected manner various facts in mechanics, light, heat, sound, electricity, and magnetism. Under the head of Natural Philosophy most of us were taught that a body falling from the vertex of an inclined plane acquires the same velocity as it would if it rolled down the plane. A considerable knowledge of mathematics was required to prove this fact, and the youthful mind could hardly see the bearing of it when it was demonstrated. We were shown what we learned to call the falling machine of Atwood, which proved simple laws with such ponderousness of structure and complexity of appliances that even the name of the machine made more impression upon the memory than the laws of which it was the servant. The brightest boys could prove that the square of the velocity of a falling body was equal to twice the acceleration of gravity multiplied by the height through which it had fallen, and the rest of us mutely followed the rule, and substituted in a formula which was forgotten as soon as the exigencies of school life were over. We also carried away vague recollections of a pump which worked by means of a curiously constructed valve. We had forgotten whether the center of gravity is where the center of pressure is applied, or where specific gravity exerts itself. We remembered a tuning-fork, an electrical machine, and a big electro-magnet which lifted the smallest boy in school, and that was all that we remembered of natural philosophy. At that very age most of us, if not all, were curious about air and water, the motions of the earth and the moon, the light of the stars, the curious manifestations of frost, fire, and electricity and magnetism. I remember how glibly we recited portions of natural philosophy where the author forgot his grim mood for a moment, his triangles and square roots, and explained in a simple manner why the rising moon appeared so large between the small branches of a wood, and why fog came up the bay when the sun went down. When we succeeded in getting the right answer to a problem we were elated and began to think that natural philosophy was not so difficult to study, after all; but these moods of elation were too often succeeded by those of blackest night and incendiary desires. In looking back, the thought comes to us that there must have been something radically wrong in such teaching; for the subject of the laws of the physical universe has such infinite possibilities and contains so much that can stimulate the imagination of even young children, that any method which represses, or does not encourage a child's desire to know the reason of things, must be radically wrong.
It must not be supposed, however, that the picture we have presented has not its bright side: there are always teachers who are especially interested in physical science, and who excite an interest in the subject among their pupils. The hour of the lecture on physics is looked forward to by the pupils of some schools with great relish, and some date their interest from the school exercises in this branch. Generally speaking, however, most men who have more than the ordinary knowledge of science have had their enthusiasm awakened out of school, and by actually working with apparatus, or handling specimens, have taught themselves.
The opponents of the study of physics in the secondary schools generally regard it as of less importance than the mathematical or grammatical studies, and class it among what they regard as superfluous subjects, the number of which has very much increased of late years. Not a few of these remember the manner in which they were taught, and have no desire that their children should repeat their experience. It is very natural also that the teacher whose training has been exclusively literary should be indisposed to teach a subject like physics, which requires a certain facility with apparatus and some inventiveness which a purely literary training has the effect of obscuring and even crushing out. Who has not seen an excellent teacher in the languages or even in mathematics fail completely before a class of boys and girls in showing some simple experiment? It is very natural that he should fail, for this facility and inventiveness of which we have spoken come, except to the few, only by practice and from an early habit of observation. More time also is consumed in getting ready for one lecture or exercise in physics than in six recitations in the straightforward subjects of language and mathematics. A refractory piece of brass, a wire wanting here and there, a shrunken bit of bladder, a broken glass tube, may involve hours' labor for one who is generally hard-worked in other ways. It is easy to theorize on the subject of teaching science, especially physical science, in the second grade of schools, but one should not forget the wearing nature of routine work which is apt to deaden one's enthusiasm. One can not expect a teacher to hold weekly talks with his pupils on force, or to rely upon treatises which are merely descriptive, or to be patient with apparatus which, by frequent use, seems almost puerile, without giving him also a comparatively rigid standard in the shape of a book by which he can advance in a more or less mechanical manner. Many teachers, therefore, comply with the letter of the law, and with one of the many text-books called Natural Philosophy shorten the popular exposition of the subject to a minimum and demand a certain number of problems under the lever, the screw, the inclined plane, and the pendulum. This mechanical teaching succeeds to a certain extent with the bright boys of some tendencies; but it fails with the great majority, who speedily get a disgust for the whole subject. To add to the teachers' difficulties, many of them have not a sufficient knowledge of the subject to enable them to courageously reject the descriptions of machines with which many text-books are filled, in which the principles are lost sight of in a multiplicity of levers, pulleys, and connecting pieces.
In teaching a language or a branch of mathematics in a grammar school, one has all his materials ready at hand, a certain author, a certain dictionary, a grammar. In teaching physical science, almost every text-book requires to be supplemented by some apparatus which is not provided with the text-book, and contrivances must be resorted to, and judgment must be used in regard to aids in teaching upon which experience seems to be very indefinite. There are wide limits in regard to the cost of this or that piece of apparatus, and difficulties in deciding between instrument-makers. Very often there is no one available to repair an instrument, and the instruction has an added tendency to become mechanical.
On the other hand, there are enthusiastic teachers who are imbued with the modern popular method of teaching physics by the aid of a lime-light stereopticon. Small appropriations are saved until an expensive instrument can be obtained; and what may be called a college course in physics is inaugurated in the second grade of schools. It is a laudable ambition to desire to illustrate the subject of physics by the method of projections; but the policy of expending from one to two hundred dollars for a lime-light for the use of a grammar or even a high school is questionable.
Professor Mayer, in his excellent little books on the experimental study of light and sound, shows how a water lantern can be constructed for three dollars, which answers every purpose; and if there is no sunlight one of the many forms of kerosene lanterns is admirable for showing diagrams, the deflections of a galvanometer, crystallizations, and minute experiments which a class could not otherwise see to advantage. With the aid of such a cheap method of projection, a grammar school master can give quite an extended course in physics with simple apparatus. He can draw his own diagrams on smoked glass, fixing the drawing by exposing it to the vapor of alcohol, which is evaporated from a shallow dish; and for the money which is expended for a lime-light apparatus enough apparatus can be bought which, supplemented by a water or a kerosene lantern, would illustrate a full course of elementary lectures on physics. In many school collections of apparatus, a few expensive instruments will be found: an air-pump; a Holtz electrical machine; a large induction coil. One or two of such instruments form the rallying point of the department of physics, and are accompanied by meager and disjointed apparatus. The student collects, so to speak, his thoughts about the picture of a complicated machine; his ideas of the pressure of gases or rarefied air are complicated by the imperfect remembrance of certain valves. Electricity of high tension means something evoked by an electrical machine. These pieces of apparatus which I have mentioned form a salient point of attack upon the system of instruction in physics too common in many schools. A good air-pump is difficult to keep in order, and finds its true place only in the private laboratory of an investigator, or in a college collection of apparatus. In the secondary grade of schools some form of Sprengel's pump, or, where there is an available head of water, an aspirator, will illustrate varying pressures sufficiently well. The new Holtz machine which schools are anxious to possess can only serve as a toy, for the theory of its working is very hard to comprehend even by those who have studied the subject in mature years.
The modern view of the physical universe is that there is no such state as rest: the particles of a gas are in an incessant state of motion, and it can be maintained that when a stone rests upon a table it is not at rest; for it is forced downward by the action of gravitation through a very small distance, and the elasticity of its support tends to move it upward through the same distance. The term statics is apt to be misleading, and the best-writers on science of to-day begin treatises on natural philosophy with the subject of dynamics or forces in motion. In no subject, however, is the division into statics and dynamics so illogical as in the subject of electricity. In most schools a student begins the study of this subject with frictional electricity and the electrical machine. An advanced student in a university pursues the opposite plan, and approaches the subject, even if it be for the first time, from the standpoint of the voltaic cell, and traces the development of the force up to the point of the generation of electricity similar to that produced by an electrical machine. Very little knowledge can be obtained from the exhibition of toys like dancing pith-balls, insulated stools, miser's plates, and apparatus for obtaining shocks.
The method of instruction in physical science, therefore, in the secondary grades of schools, seems to me to be too costly and not sufficiently logical. The remedy does not consist in curtailing the amount of attention paid to the subject in the lower schools, or in relegating it to a more advanced period of education. It is more reasonably embraced in leading teachers to seek simpler methods of instruction, simpler apparatus, and to avoid abstruse conceptions, and the solution of mechanical problems for which mere formulas are given. It would be well, also, if the best students are led to experiment themselves, and are stimulated to observe. This is hardly possible in crowded grammar schools; but the excellent little treatises of Professor Mayer on experimental physics would lead many children, under proper encouragement from their teachers, to try simple experiments at home.
An ideal method of teaching physics in the secondary grade of schools would consist in developing the whole subject from the standpoint of motion, insisting upon the larger facts, correlating them as far as possible, and neglecting special applications and special facts. A number of interesting experiments can show that work must be done in all cases to produce work, and that motion can be changed into heat, and heat into motion. The student's mind should be tempted to take, at the very beginning of his study of the subject, an extended view of the application of the law of the conservation of energy. While treating the subject of force, a little descriptive astronomy can be given which will aid in stimulating the imagination. The subjects of heat and acoustics can be taught purely under the head of mechanics, with a variety of most interesting and simple experiments. I am inclined to place the subject of electricity and magnetism under the same head; and, beginning with the fact that electricity is generated by a voltaic cell, I should trace its simple manifestations until they conduct one to the law that all motion can be converted into electricity, and that electricity can be entirely converted again into heat and light. Having then shown that light can be produced by motion, the undulatory theory can be cautiously introduced. As a review of the subject of physics, one could take as a text the impossibility of perpetual motion, and enforce it with a variety of illustrations. The utility of the study of physics in the grammar schools is often questioned, and indeed the larger question of the value of scientific training except to the few in the world at large is often mooted. There is no doubt that the study of the humanities, in which the great story of men's deeds in the past is recorded, will always prove the most fascinating to the majority; and it can be maintained with reason that those subjects which readily excite an interest in the largest number will prove the readiest means of intellectual training. Science is regarded by many scholars merely as a practical branch of human knowledge, and, although its great value in contributing to the good of the world is acknowledged, yet its study is regarded as inferior in intellectual results to that of language or philosophy. It can not be denied, however, that the study of physical science gives a certain definiteness to our modes of thinking, even if it will not be granted that it affords a better method of intellectual training than philological study. It supplies a tonic which minds much accustomed, from the exclusive study of language, to take things for granted and to look no further than the grammar and dictionary stand much in need of, and also corrects a certain credulity and superstition which is rampant, even in our time, and to which it is well to devote a few words in connection with the subject of scientific training. There is a strong undercurrent of superstition and belief in supersensible or wonderful and not-to-be-explained marvels which makes its way beneath the crust of society. Occasionally it bursts forth in so-called manifestations of spiritualism and animal magnetism, or belief in mesmerism and clairvoyance. There is hardly a family of which some member has not applied to a clairvoyant for relief in diseases which the regular practitioner has failed to treat successfully. A literary education does not cope successfully with the insidious advances of this form of ignorance; for the very element of education which can do so is not generally cultivated among even so-called liberally educated persons. This lost element is the spirit of investigation. The students who come to a physical laboratory for the first time can be rapidly classified into three classes: 1. Those who can reason from A to B over what may be termed a straight line with considerable ease. 2. Those who naturally reverse their process of reasoning and test the way from B to A; this is a rarer class of minds. Copernicus was unable to explain the motions of the planets by supposing that all the visible stars revolved around the earth; he reversed his process of reasoning, and explained the facts by supposing the earth to turn and the stars to remain at rest. Kant, in his "Critique of Pure Reason," speaks of the revolution which he had brought about in philosophy, and likens it to the logical process which led Copernicus to his discovery. "Hitherto," he says, "it had been assumed that all our knowledge must regulate itself according to the objects; but all attempts to make anything out of them a priori, through notions whereby our knowledge might be enlarged, proved, under this supposition, abortive. Let us, then, try for once whether we do not succeed better with the problems of metaphysics, by assuming that the objects must regulate themselves according to our knowledge, a mode of viewing the subject which accords so much better with the desired possibility of a knowledge of them a priori, which must decide something concerning objects before they are given us." In practical matters this process of reversals is often exemplified; the inventor of the sewing-machine finds that his needle will not work with the eye at one end, and accordingly reverses its position and is successful. 3. The third class comprises those who may be said to think in directions at right angles to their previous method of thinking, and there may be minds which possess what is analogous to the 4th dimension in space — an ability to think in all azimuths. It is strange that there are so few psychological impostors in the world; for the first class of minds, those who only think from A to B when a new class of facts are presented to them, is very large. An ingenious man can make a small magnetic motor which apparently runs with only the assistance of permanent magnets, and by means of extremely small clockwork maintain the motion beyond the period which a mind of class 1 is willing to give to an observation. It would naturally occur to such a mind to take the motor to pieces and examine the casings or box. If it finds nothing, and perceives that, when the apparatus is put together and is placed by the inventor on his table, it still runs, the investigation ceases, and another story confirms the previous rumor of a new marvel. A mind of class 2 goes over the same process of reasoning, and moves the instrument to different points for fear of concealed mechanism under the table or in the wall. A skillful manipulator, however, can still edge the motor to a third or fourth position, where other concealed clockwork can be taken advantage of, and in this way exhaust the number of what may be termed linear combinations of the investigator. The success of impostors in spiritualism and of the fabricators of new motors which are built to delude people resides in this, that they restrict the liberty of this system of reversals, or the spirit of investigation.
Any plan of education which prevents a man or woman from becoming the dupe of those who pretend to use natural or supernatural forces is to be commended. One of the quickest ways of training the mind in the logical process which I have indicated is to undertake some simple investigation in physics. Here mere observation is combined with a careful study of the interaction of various forces, and the mind must assign a logical weight to different observations. One truth, moreover, is forcibly brought forward — that, generally speaking, a number of observations under varying conditions must be made to prove the correctness of any result. The man who has been through the process will not be found among those who are convinced by a single manifestation of clairvoyance or of spiritualism. He will not spread the stories of a wonderful new motor until he has put it to an exhaustive test.
It would be well if our common schools made some provision for a certain amount of experimental work in physics to illustrate this method of studying. A great deal of education is comprised in the knowledge of how to change the conditions of an experiment in the process which I have termed a reversal, and also in the process of depending only upon a number of observations taken under different conditions. It would certainly be a great boon to the world if the general level of scientific education could thus be raised, so that each young man or young woman, when he or she issues from school doors, should have enough definite knowledge of the great laws of the physical universe to instantly denounce blue-glass theories and attempts at perpetual motion, not from the pride of knowledge, but from the feeling that error, credulity, and superstition should be combated with truth.