To kindle inspiration and enthusiasm nothing can equal the contact in lectures with others, preferably leaders in their profession, but at least men who possess one of these qualities. Such contacts need not be frequent; indeed, they should not be. The speaker is apt to make more effort, the student to be more responsive, if such occasions are relatively rare. Even thus, although real information is imparted at such a time, it is seldom acquired. However, perspective is furnished, interest stimulated, and the occasion enjoyed.
Limitations of exclusive use of each method
For the real acquisition of scientific information, the great method is the working out of a laboratory exercise and pertinent problems, with informal guidance in the atmosphere of active study and discussion engendered among a small group,—the laboratory method. Taken alone, it is apt to become mechanical and uninteresting and the outlook to be obscured by details. Lectures, especially demonstration lectures, are needed to vitalize and inspire. Moreover, many of the most vivid illustrations of physical principles that occur on every hand to focus the popular attention are never met with in the college course because they are unsuited for inexperienced hands or not readily amenable to quantitative experimentation. The more informally such demonstrations can be conducted, the more enthusiastically they are received.
Aims of the laboratory method
With regard to laboratory work, accuracy in moderate degree is important, but too great insistence upon it is apt to overshadow the higher aim; namely, that of the analysis of the phenomena themselves. A determination of the pressure coefficient of a gas to half a per cent, accompanied by a clear visualization of the mechanism by which a gas exerts a pressure and a usable identification of temperature with kinetic agitation, would seem preferable to an experimental error of a tenth per cent which may be exacted which is unaccompanied by these inspiring and rather modern points of view. Especially in electricity is a familiarity with the essentials of the modern theories important. Here supplementary lectures are of great necessity, for no textbook keeps pace with progress in this tremendously important field. Problem solving with class discussion is absolutely essential, and should occupy at least one third of the entire time. In no other way can one be convinced that the student is doing anything more than committing to memory, or blindly following directions with no reaction of his own.
Value of the supplementary lecture
The incorporation recently of this idea into the courses at the University of Chicago has been very successful. Five sections which are under different instructors are combined one day a week at an hour when there are no other university engagements, for a lecture demonstration. This is given by a senior member of the staff whenever possible. The other meetings during the week are conducted by the individual instructors and consist of two two-hour laboratory periods and two class periods that usually run into somewhat over one hour each. These sections are limited to twenty-five, and a smaller number than this would be desirable. The responsibility for the course rests naturally upon the individual instructors of these small sections. These men also share in the demonstration work, since each is usually an enthusiast in some particular field and will make a great effort in his own specialty to give a successful popular presentation of the important ideas involved. The enthusiasm which this plan has engendered is very great. Attendance is crowded and there is always a row of visitors, teachers of the vicinity, advanced students in other fields of work, or undergraduates brought in by members of the class. These latter especially are encouraged, as this does much to offset current ideas that physics is a subject of unmitigated severity. The particular topics put into these demonstrations will be discussed in paragraphs below, which take up in more detail the organization of the special subdivisions of the material in a general physics course.
Mechanics a stumbling block—How to meet the difficulty
Mechanics is a stumbling block at the outset. As we have indicated above, it must form the beginning of any course that is analytic in aim. There is no question of sidestepping the difficulty: it must be surmounted. A judicious weeding during the first week is the initial part of the plan. Interest may be aroused at once in the demonstration lectures by mechanical tricks that show apparent violations of Newton's Laws. These group around the type of experiment which shows a modification of the natural uniform rectilinear motion of any object by some hidden force, most often a concealed magnetic field. The instinctive adherence of every one to Newton's dynamic definition, that acceleration defies the ratio of force to inertia, is made obvious by the amusement with which a trick in apparent defiance of this principle is greeted. Informality of discussion in such experiments, questions on the part of the instructor that are more than rhetorical, and volunteer answers and comment from the class increase the vividness of the impressions. A mechanical adaptation of the "monkey on the string" problem, using little electric hoists or clockworks, introduces interesting discussion of the third law in conjunction with the second. A toy cannon and target mounted on easily rolling carriages bring in the similar ideas where impulses rather than forces alone can be measured.
There follow, then, the laboratory experiments of the Atwood machine and the force table, where quantitative results are demanded. It is desirable to have these experiments at least worked by the class in unison. Whatever may be the exigencies of numbers and apparatus equipment that prevent it later, these introductions should be given to and discussed by all together. In the nature of things, fortunately, this is possible. A single Atwood machine will give traces for all in a short time under the guidance of the instructor. The force table experiment is nine-tenths calculation, and verifications may be made for a large number in a short time. Searching problems and discussion are instigated at once, and the notion of rotational equilibrium and force moments brought in. Because of the very great difficulty seeming to attach to force resolutions, demonstration experiments and problems using a bridge structure, such as the Harvard experimental truss, will amply repay the time invested. Another experiment here, which makes analysis of the practice of weighing, is possible, although there will be divergence almost at once due to the personality of the instructor and the equipment by which he finds himself limited. The early introduction of moments is important, however, because it seems as if a great amount of unnecessary confusion on this topic is continually cropping out later. At this point, if limitations of apparatus present a difficulty, a group of more or less independent experiments may be started. Ideas of energy may be illustrated in the determination of the efficiency and the horse power of simple machines, such as water motors, pulleys, and even small gas or steam engines.