LITERARY NOTICES. 



125 



Van Nostrand's Science Series, No. 66, 

 Dtnamo-Electric Machinery. A series 

 of Lectures by Syltanus P. Thompson, 

 Professor of Experimental Pliysics iu 

 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 

 80 rapidly attained prominence that few 

 persons have yet been able to gain an ade- 

 quate idea of its forms or principles. In 

 the first of these lectures, on " The Dj-namo 

 in Theory," Professor Thompson proposed a 

 division of dynamos into three classes, ac- 

 cording 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 eSiciency will be in- 

 creased 71* times. Under " The Dynamo in 

 Practice " he has described t]i3 arrangement 

 of the several elements as they appear in 

 the machines of a large number of promi- 

 nent 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 en- 

 ergy 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 W. Bemis, 

 A. B. Pp. 25. Price, 25 cents. Balti- 

 more : Johns Hopkins University. 



These pamphlets belong tothe series of 

 "Johns Hopkins University Studies in His- 

 torical and Political Science," and speak 

 well for the practical value of the plan on 

 which the studies are based. The paper on 

 Hlinois 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 Eng- 

 land plan, with the township as the princi- 

 pal factor. The two systems have met and 

 struggled for the mastery; the New Eng- 

 land plan is prevailing, and now only about 

 one fifth of the one hundred and two coun- 

 ties in the State cling to the old county sys- 

 tem. 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 par- 

 tition of power, for the terms of which we 

 must refer to the pamphlet. The organiza- 

 tion in Michigan is a transplantation of the 

 New England system, with unimportant dif- 

 ferences. In Mr. Bemis's paper, the Michi- 

 gan system is compared with that of each of 

 the older Eastern States and with the sys- 

 tems which have been or are being adopted 

 in the other States of the West and North- 

 west, 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. Biji- 

 swanger & 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, phi- 

 losophy, 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 un- 

 trammeled, and their literature is rich in 

 the fruits of their many-sided work, partic- 

 ularly in philosophy, ethics, mathematics, 

 astronomy, and hygiene. Down to the thir- 

 teenth 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 contrib- 

 uted much to the revival of learning in the 

 West, for they understood the languages in 



