400 Scientific Intelligence. 



her of the Philosophical Magazine is a very suggestive one by- 

 Prof. W. H. Bragg and Mr. R. D. Kleeman on this subject. 

 They conclude in the main that (l) the range varies inversely as 

 the pressure ; (2) that the total number of ions set free in a gas 

 is independent of the pressure, but is different in different gases. 

 — Phil. Mag., April, 1906. ,t. t. 



11. Nucleatiori of the Atmosphere. — The subject of the nuclea- 

 tion of the atmosphere, discussed by C. Barns in a series of papers 

 published in this Journal (volumes xiii to xx) is treated at length 

 by the same author in the following exhaustive memoirs : 



A Continuous Record of Atmospheric Nucleation ; pp. xvi, 226, 

 from volume xxxiv of the Smithsonian Contributions to Knowl- 

 edge. The investigation was carried on with the aid of a grant 

 from the Hodgkins Fund. 



The Nucleation of the Uncontaminated Atmosphere; pp. xii,. 

 152. Publication No. 40 of the Carnegie Institution of Washingon 



II. Geology and Mineralogy. 



1. Geology ; by Thomas C. Chamberlin and Rollin D. 

 Salisbury. In three volumes, Vol. II, Earth History, Genesis- 

 Paleozoic, pp. xxvi, 677 and index, with geological map of the 

 United States compiled by Bailey Willis, numerous paleogeo- 

 graphic maps and other illustrations. Vol. Ill, Earth History, 

 Mesozoic- Cenozoic, pp. xi, 578 and index to vols, i, ii, iii. Maps 

 and illustrations, as in the preceding volume. New York, 1906 

 (American Science Series, Advanced Course. Henry Holt & Co.). 

 — Since the publication of Yol. I of this work in 1904, with its 

 able and original discussions of earth processes, every geologist 

 has awaited with much interest the completion of the series. 

 This interest has been justified, for the volumes now issued are 

 conspicuous, even more than the first, for the many original 

 points of view and the radical departure from the older manuals 

 both in methods and subject matter. This series will doubtless 

 give a marked stimulus to investigation for the forthcoming 

 decade. This is partly due to the fact that the volumes look 

 forward rather than backward, an unusually large place being 

 given to working hypotheses, while unsolved problems ai'e 

 frankly recognized and the student is carried along with the 

 investigator to the still debatable ground. 



The chief innovations' are found in the chapters devoted to 

 "Hypotheses of Earth Origin" (81 pp.), and "Hypothetical 

 Stages leading up to the known eras" (50 pp.). The Proterozoic, 

 a name long since proposed by Irving, is used as the approximate 

 equivalent of the Algonkian and 55 pages are given to this era. 

 Ordovician is fully adopted in place of the long-contested name 

 of Lower Silurian ; the Subcarboniferous for the first time in a 

 text-book is given the dignity of a separate period of equal rank 

 with the Devonian, and called the Mississippian ; the true Car- 

 boniferous becoming the Pennsylvania!!. The lower Cretaceous 



