250 



THE POPULAR SCIENCE MONTHLY. 



under the necessity of taking notes, is often 

 prevented from seeing what takes place on 

 the lecture-table. The book is intended to 

 give concisely the facts essential to intelli- 

 gent work in the laboratory, that the stu- 

 dent may have more leisure for observation 

 in the lecture-room. The work shows the 

 divisions of the bases and the acids into 

 groups, as well as the means of detecting 

 them ; also directions for the examination 

 of specimens, the reactions of various sub- 

 stances under different circumstances, and 

 the method of treating them with water 

 and with acids. 



Deutsche Rundschau. Herausgegaben von 

 Julius Rodenberg. Monthly. 10 per 

 annum. 



This is the first number of a Review, 

 intended to occupy, in German periodical 

 literature, about the same rank that is held 

 by the Revue des Deux Monies in the peri- 

 odical literature of France. Like its French 

 prototype, it will contain novelettes and con- 

 tinued stories, historical sketches, political 

 articles, scientific essays, poems, etc., to- 

 gether with book reviews, criticisms of 

 music and the drama, and political notes. 

 The scientific article in the present number 

 is entitled " Botanical Problems," and is 

 written by Prof. Ferd. Cohn, of Breslau. 

 Stechert & Wolff, 4 Bond Street, New York, 

 receive subscriptions for the Deutsche Rund- 

 schau in the United States. 



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Lecture Notes on Quantitative Analysis 

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Insanity and Disease (Tourtellot). Pp. 15. 



Catalogue of Plants (Wheeler's Expedi- 

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MISCELLANY. 



Does the Earth rotate at a ! inform 



UatC 1 In the September number of Silli- 

 man , s Journal, we find a remarkable paper 

 by Prof. Newcomb, of the Naval Observa- 

 tory, Washington, to the conclusions of 

 which we wish to call the attention of our 

 readers. 



Prof. Newcomb, who has for some time 

 been engaged on the most difficult problem 

 of celestial mechanics the " Theory of the 

 Moon's Motion" published, in 1870, a 

 paper referring to some of the difficulties 

 in this theory. He has treated the lunar 

 theory in quite an original and exhaustive 

 manner, and, in the course of his investiga- 

 tions, arrived at the fact that there were 

 certain outstanding differences between the- 

 ory and observation which had not yet 

 been accounted for by the gravitation of 

 the known bodies of the solar system. Prof. 

 Newcomb suggested that there were only 

 three possible explanations of the discrep- 

 ancy : 1. The mathematical analysis was not 

 sufficiently extended ; 2. The motion of the 

 moon was affected by some force different 

 from gravitation ; 3. The time of the earth's 

 rotation on its axis was not constant. 



The second hypothesis Prof. Newcomb 

 showed was not at all probable, since the 

 effects of a force other than gravitation 

 would produce variations of a different 

 kind from the ones actually noticed : the 

 first hypothesis Prof. Newcomb has, since 

 1870, been engaged in testing, and his re- 

 searches have convinced him that analysis 

 has taken cognizance of every important in- 

 equality in the moon's motion. This makes 

 it necessary to examine rigorously the third 

 hypothesis, viz., that the earth's time of ro- 

 tation on its axis is not strictly uniform. 



This explanation is, at first sight, some- 

 what startling, since the absolute uniform- 

 ity of the sidereal day has long been sup- 

 posed certain. Prof. Newcomb's researches 

 in 1870 led him, however, to the conclusion 

 that the earth had been rotating somewhat 

 slower than the average rate for ten or 

 twenty years previous to 1860 ; that about 

 1860 the rotation was accelerated, so that 

 there was a gain of at least a second per 

 annum till about 1872. 



This hypothesis would, we must re- 



