Page:Popular Science Monthly Volume 43.djvu/403

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TEACHING PHYSICS

be without, and no scientific man dare to be without, and to those who have the ability, the opportunity, and the desire, a trustworthy foundation on which to base their further studies.

The scheme almost necessarily formed itself into the following: The student attends a lecture every morning, except Saturday, at ten o'clock. These lectures, in the present case, are about seventy in number. At eleven o'clock he goes into the laboratory, provided with a few tools; there he finds the necessary material for making apparatus relating to the lecture. He has also printed instructions directing him how to make and how to use the apparatus when made. He finds also working models of such apparatus for his guidance. These instructions he carries out under the supervision and advice of a skilled assistant.

The instruments the student of average skill can and does make under proper instruction with these means are far more accurate than those he is at all likely to be able to buy. I do not say that his divided circles will be as accurate as those of Troughton and Sims, nor will his spectroscope compare with one of Hilger's, nor his resistance coils with those of Elliott, nor his barometer with the one at Kew; but I do say that his barometer is a far more exact instrument than one for which he would have to give several pounds; that his spectroscope will divide the sodium line; that his coils are true to the thousandth of their nominal value; that he can determine the wave-length of light to within 1/1000, of the truth, the specific heat of a metal to 1/100, and the length of a sound-wave to 1/200 of the truth. The only bought instrument of precision which the student uses in the elementary course is the balance. He has generally, however, acquired some skill with this, and in the manipulation of glass, in the chemical laboratory.

Starting with a tuning fork which is given to him, and the monochord which he makes, the student is able to verify the intervals of the gamut as dependent on length of string. He then examines the effects of variation of diameter, of tension, and of weight of the string.

Tuning forks are, however, seldom exact. The actual pitch of the fork is found by the method of sinuosities. A smoked glass plate is dropped in front of a style on the fork, and so the fork writes its own number. Hence, by means of the length of the resonant cavity, the velocity of sound in air is obtained with some accuracy, and by the method of longitudinal vibrations the velocity in wood, glass, and brass, etc., follows. The rule of the transverse vibrations of rods is examined. The production of harmonics on strings, rods, and in tubes is shown, and a number of experiments follow concerning the velocity of sound in different gases as determined by dust figures.