and must be studied by the individual in the laboratory. In any elementary course they are relatively few in number, and even in a fully equipped laboratory are rarely shown to any but the most advanced students.
The value of the lecture demonstrations must again be emphasized in connection with the fact that a number of the most important phenomena, such, for example, as those of electricity, make no direct or at least no unmistakable appeal to our senses, and are apprehended only by some very ordinary occurrence like the movement of two objects in the field of vision. For example, a discovery of such immense importance as that of current induction by Faraday was evidenced to him only by the minute and momentary motion of a needle over a scale. And since throughout the whole range of physics the measurements are rarely direct, so that the interpretation of the reading of any apparatus is of more importance than making the reading, the first introduction to physical apparatus may often better be given on the lecture table than in the laboratory.
In turn with this brief discussion of the use of the text-book and the lecture demonstration the peculiar function of the physical laboratory deserves careful examination. We remark first of all that because experimental examination and dissection are essential to the teaching of biology it does not therefore follow that the laboratory teaching of physics is essential; nor because laboratory manipulation and observation are necessary to the teaching of chemistry does it follow that laboratory manipulation and observation must be necessary and indispensable to the teaching of physics. In such a statement there is not, however, intended the faintest suggestion that work in the physical laboratory is anything but useful and necessary, but rather to emphasize how widely the function of the physical laboratory differs from that of the chemical and biological laboratories. Physics is an exact science (though just what that means can be learned only in a physical laboratory) while biology is not so at all and chemistry is but to a limited degree.
Biology may be said to have formulated a few general laws, such, for example, as the law of biogenesis or the doctrine that life is generated by living beings only; the law of natural selection or the doctrine that the structure and function of any organism are the results of the survival of those members of a class which were best fitted to their surroundings; the law of prepotency which asserts that the probability of any organism approximating to its type increases with the number of its ancestors of that type. None of these laws contain any quantitative elements and consequently are never made the subject of laboratory measurements. As the rest of the science is for the most part a system of more or less rational classification of multitudinous forms of life,
