302 Notices respecting New Books. 



Lecture-notes on Physics. By Alfred M. Mayer, Ph.D., Professor 

 of Physics in the Lehigh University, Bethlehem., Pa. — Parti. Phi- 

 ladelphia: from the Journal of the Franklin Institute, 1868 (pp. 

 112). 



This is scarcely to be called a book, it is much more nearly a 

 synopsis of the subject, with disquisitions inserted on the points 

 of chief interest, as well as extracts from other writers. The sub- 

 jects discussed in this first part are the following : — Introduction 

 to the Inductive method, Instruments for precise measurements, 

 Methods of Precision (e. g. the method of least squares), Methods of 

 determining the laws of phenomena, the General Properties of Mat- 

 ter, and Capillary Attraction. The author gives a very good resume" 

 of the leading facts under each of these heads, and, more than that, 

 gives many references that may be useful to those who wish to go 

 further into the subject than he is able to take them. The follow- 

 ing short extract will perhaps convey a better notion of the form of 

 the book than an elaborate description. Under the head of instru- 

 ments for measuring lengths, the author gives an account of the 

 micrometer-screw. This he does as follows : — 



" Micrometer- screw (from Greek fjuapos small, and fierpov a mea- 

 sure) consists of a screw with a large circular head, whose circum- 

 ference is divided into a certain number of equal parts. Suppose 

 the screw has fifty threads to the inch, and that its circular plate, 

 which rotates with it, is divided into two hundred parts ; then if the 

 screw is turned a whole revolution, it will advance, in the block 

 in which it turns, g^th of an inch ; but if the head is revolved only 

 through -2017th of a revolution, the screw will advance the — — ± — th of 

 an inch. With a good micrometer-screw we can measure accu- 

 rately the y^^th of a millimetre, or about the 4 th of an 

 inch. 



" (Large model exhibited, also the instrument itself in various 

 forms.)" (P. 16.) 



We have only to add that, allowance being made for the imper- 

 fections necessarily arising from the form of the book, it seems to 

 us well done, and to be the work of a man who has an accurate and 

 extensive acquaintance with his subject. 



Theory of Existence. — Part I. devoted to the enunciation of the laws 

 which determine the motions that result from the collision of ponde- 

 rable bodies. By Elias Dexter. New York : Edward Dexter, 

 564 Broadway, 1869. Pp.155. 



The object of this first part of the above work is to dispel what 

 the author regards as prevalent errors about the laws of motion and 

 other fundamental points of mechanical philosophy. He aspires to 

 take the same place with respect to Newton and Laplace that Galileo 

 took with respect to the Aristotelians of his day. How the author 

 may deal with the General Theory of Existence, when he gets to it, 

 we do not know ; but his power of dealing with elementary dyna- 



