Page:Popular Science Monthly Volume 37.djvu/361

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ing to a suggestion found in Gage's Elements of Physics, illustrated well the advantage of requiring pupils to make apparatus, even when free access is had to that made by the instrument-maker. A piece of wood cut from the spoke of an old wheel was loaded at one end with lead, so as to make it stand upright. It was immersed in rain-water, and the water-level on it marked 1,000. By means of a Baumæ's hydrometer the level of 900 was found, and distances, equal to the distance between the two marks, laid off above and below. Much to the boy's surprise, the hydrometer thus graduated would by no means coincide with his PSM V37 D361 Hydrometer.jpgFig. 2.—Hydrometer. Baumé. He attributed the error to the absorption of the fluids by the wood, and set to work to make another, taking care this time to rub the wood with beeswax, to render it impervious to liquids; but his second graduation was hardly more satisfactory than the first. He then put on a piece of cork for a float, the wood having failed to keep an upright position in all liquids, and graduated his hydrometer by means of different liquids whose densities had been found with the Baumæ hydrometer, and at last discovered that the divisions were not equal. This piece of work, represented in Fig. 2, consumed all the boy's afternoons for a week; but I saw the effect of it in increased carefulness, and consequently greater accuracy in his subsequent work, and, what was still more important, in increased thoughtfulness.

A condenser for use in distilling water was made after the pattern of Liebig's. The outside tube was made by boring a round piece of wood, ten inches long and two inches in diameter, through with an inch auger. The inside tube, and those for entrance of cold water and exit of hot water, were made of reeds. A bottle served for the still, and the whole was supported on a neat wooden stand.

Such work undoubtedly requires much energy on the part of the teacher, for his suggestions will be needed and asked for many times during the week. But if he is a mere college or high-school graduate who has gained his knowledge of science from the lectures and experiments of the professor, he will find this work of making home-made apparatus even more beneficial to himself than it is to the pupils. He will by means of it have much light thrown upon obscure places, and will accordingly