in the wooden shutter of his window in order to admit a narrow beam of light which was to be dispersed into a spectrum by his prism. Even as late as the middle of the nineteenth century the celebrated determination of the velocity of light was made by Foucault, who is said to have been so poor that he was obliged to hire a pair of telescopes at an optician's and to make the experiment in his own rooms. In fact, physical research had reached a very great extension before the provision of special buildings in which to carry it on had been thought of, and these were first provided in connection with instruction. It was not until 1874 that the celebrated Cavendish laboratory was completed at the University of Cambridge, and it is worth remarking that this great laboratory, out of which has proceeded a large number of the most remarkable modern discoveries in physics, was built at a cost of little over $40,000. It is interesting to know that the introduction of laboratory studies at Cambridge was attended with much shaking of heads and it seemed necessary to Maxwell, the first professor of experimental physics there, to justify its introduction in his opening lecture. "But what," he says, "will be the effect on the university, if men pursuing that course of reading which has produced so many distinguished wranglers turn aside to work experiments? Will not their attendance at the laboratory count not merely as time withdrawn from their more legitimate studies, but as the introduction of a disturbing element, tainting their mathematical conceptions with material imagery and sapping their faith in the formulas of the text-books?" A more amusing doubt was that expressed by Todhunter, himself a distinguished mathematician and student of natural phenomena. "What is the use," said he, "of a student's confirming a physical phenomenon by an observation in the laboratory? If he will not believe the statement of his tutor, who is presumably a gentleman of exemplary character in holy orders, what use can there be in his repeating the experiment for himself?" It is needless to say that this point of view has long since passed into oblivion and the strong point of the laboratory is that it enables the student to himself verify the laws of nature quite independently of the statements of any authority whatever, however respectable.
The purposes of our laboratories then are twofold. First, in them we teach our students the use and manipulation of instruments and the methods for the precise verification of physical laws. In this way the student becomes accustomed to habits of accuracy and the reporting of what he actually sees without the aid of the varnish of imagination and unaffected by any prejudices as to what result he expected to get. We thus have an education in morals which is hard to equal in any other part of education. As a simple example let us consider the method in which the student studies the motion of the pendulum in the elementary laboratory. Instead of measuring the time of its swing by his
