Geology and Natural History. 465 



should emit only (3 and y rays. The ft ra} T s should decay to half 

 value in about forty years. The radium E should emit only a 

 rays and its value should fall to half value in about one year. 

 Professor Rutherford considers whether these two products have 

 been identified by various observers. — Phil. Mag., Nov. 1904, pp. 

 636-650. J. t. 



14. Text-book of General Physies for High Schools and Col- 

 leges; by Joseph S. Ames. Ph.D. 768 pp. (American Book Com- 

 pany.) — In this extensive book there are many excellencies at 

 once apparent to a reviewer. The print is all that could be desired 

 and the diagrams are not only clear but, as a rule, exceptionally 

 well designed. So too the pictures, which are presented in ample 

 but not excessive numbers, are good and well chosen. An excel- 

 lent feature, also, is the short bibliographies at the ends of many 

 of the sections, which may prove especially helpful to a reader 

 remote from a large library. 



If we look for a distinguishing characteristic in this work with 

 respect to its predecessors in the same field, we should doubtless find 

 it an unusually frank effort to teach physics by a mere extension 

 of the individual experience of the student. As this is a method 

 which, to many teachers, seems beset with formidable difficulties, 

 one turns with natural interest to the treatment of mechanics, 

 here extended beyond the usual proportion. The definition of 

 Mechanics (p. 83) takes the unusual form " the science of the 

 inertia of matter." Nowhere, however, does the term inertia 

 appear to be defined or used in a quantitative sense. The only 

 definition (p. 14) is given in the following words : " If the motion of 

 a body is changed in any way by means of our muscles, we are 

 conscious of the sensation of force ; and the name ' inertia' is 

 given to that property of the body owing to which this is trne." 

 Mass is defined (p. 60) as pure number, consequently force is (p. 

 60) asserted to be a magnitude of the same kind as acceleration. 

 Such inconsistencies, however, will doubtless be eliminated in 

 revision. c. s. h. 



I. Geology and Natueal Histoey. 



1. The Stratigraphy and Paleontology of the Niagara of 

 Northern Indiana. Stratigraphy, by E. M. Kindle : Paleontol- 

 ogy, by E. M. Kindle and C. L. JBreger. Twenty-eighth Annual 

 Report of the Geological Survey of Indiana, 1904, pp. 397-486, 

 pis. 1-25. — This small but important work treats of an area in 

 which detailed stratigraphic and paleontologic work is very 

 desirable because of the present great interest in the Cincinnati 

 axis in relation to the distribution of Silurian faunas. 



The Niagaran formations of northern Indiana are very largely 

 covered by drift, so that no complete sections are shown. Well- 

 borings indicate that the thickness for the entire Niagaran lime- 

 stones, principally magnesian, varies between 250 and 500 feet. 

 Proximit} r to land is indicated by the considerable variation in 



