Page:Popular Science Monthly Volume 24.djvu/135

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Van Nostrand's Science Series, No. 66, Dynamo-Electric Machinery. A series of Lectures by Sylyanus P. Thompson, Professor of Experimental Physics in University College, Bristol. New York: D. Van Nostrand. Pp. 218. Price, 50 cents.

This latest addition to the Science Series deals with a variety of machine "which has so rapidly attained prominence that few persons have yet been able to gain an adequate idea of its forms or principles. In the first of these lectures, on "The Dynamo in Theory," Professor Thompson proposed a division of dynamos into three classes, according to the movement of their armatures in the field of electrical force. He then took up the conditions on which the amount of force generated depends, and showed how far the fulfillment of each is compatible with fulfillment of the others. In respect to the condition of size, he calculates that, if the size of a machine is increased n times in linear dimensions, the efficiency will be increased n5 times. Under "The Dynamo in Practice" he has described the arrangement of the several elements as they appear in the machines of a large number of prominent electricians. The third lecture sets forth the principles on which is based the employment of the dynamo in converting the energy of electric currents into the energy of mechanical motion, and contains a demonstration of the mathematical law of efficiency of the dynamo as a motor. The volume is well supplied with illustrations.

Local Government in Illinois. By Albert Shaw, A. B.; and Local Government in Pennsylvania. By E. R. L. Gould, A. B. Pp. 37. Price, 30 cents. Local Government in Michigan and the Northwest. By Edward TV Bemis, A. B. Pp. 25. Price, 25 cents. Baltimore: Johns Hopkins University.

These pamphlets belong to the series of "Johns Hopkins University Studies in Historical and Political Science," and speak well for the practical value of the plan on which the studies are based. The paper on Illinois shows how the southern counties of that State, being settled from the South, were organized on the Virginia plan, in which the county is the chief factor and the township is insignificant; while the northern counties, settled later from New England, were organized on the New England plan, with the township as the principal factor. The two systems have met and struggled for the mastery; the New England plan is prevailing, and now only about one fifth of the one hundred and two counties in the State cling to the old county system. The history of the development of the Pennsylvania system is more complicated. As it stands, it occupies the middle ground between the New England township and the Southern county systems, and aims at a partition of power, for the terms of which we must refer to the pamphlet. The organization in Michigan is a transplantation of the New England system, with unimportant differences. In Mr. Bemis's paper, the Michigan system is compared with that of each of the older Eastern States and with the systems which have been or are being adopted in the other States of the "West and Northwest, including the newer Territories; and the gradual introduction and growth of the township system in the Southern States is noticed.

The Sciences among the Jews before and during the Middle Ages. By M. J. Schleiden, Ph. D. Baltimore: D. Binswanger & Co. Pp. 64.

Four editions of this essay have been published in Germany, but this is the first time it has been given in an English dress. It presents, in a rapid view, the record of what the Jews achieved for the advancement of mankind during the period indicated in the title, by their labors in literature, philosophy, science, and art. Their schools in Europe were, it is claimed, among the best of the period, and were attended even by the Christian clergy, because they furnished almost the only means of mental culture. Having no doctrinal theology, they were able to pursue every branch of study untrammeled, and their literature is rich in the fruits cf their many-sided work, particularly in philosophy, ethics, mathematics, astronomy, and hygiene. Down to the thirteenth century, they "far surpassed their Christian contemporaries, as well in point of intellect as in all the sciences having an important bearing on life." They contributed much to the revival of learning in the West, for they understood the languages in