332 Scientific Intelligence. 



is the only conceivable one, are questions which only time and 

 careful criticism can settle. But in any event the work is a very 

 remarkable one and will doubtless receive the careful attention 

 of mathematical physicists both on account of the distinguished 

 reputation of the author and of the extraordinary results which 

 he has obtained. The theory assumes, as the substructure of the 

 universe, a system of unifoi'm spherical grains of changeless 

 shape and size, so close that they cannot change their neighbors 

 but are continually in relative motion with each other. Where the 

 grains are in normal piling the properties of the medium can (by 

 properly choosing the diameter, mean relative velocity, and mean 

 path of the grains) be made identical with those of the ether 

 within the limits of observational accuracy. If, in any space, the 

 number of grains is less than in normal piling, such " negative 

 inequalities " will move without resistance through the medium, 

 will possess an apparent mass and will attract each other with a 

 force varying inversely as the square of the distance ; these are 

 therefore taken to represent the molecules of ordinary matter. 

 In a similar manner, electrical changes are accounted for by a 

 different sort of inequality in the piling of the grains, and the 

 mechanical structure of the granular medium is shown to be 

 capable of accounting for many of the phenomena of electricity 

 and of light. Like Professor Reynolds' other works, the memoir 

 is throughout marked by great originality of thought and ana- 

 lytical skill. H. A. B. 



II. Geology and Minekalogy. 



]. IT. S. Geological Su7^vey ; C. D. Walcott, Director. — The 

 following publications have recently been issued : 



Twenty-third Annual Report, 1901-02, 206 pp., 26 pis. 

 436 persons are now on the roster of the Geological Survey and 

 the appropriation for 1901-02 was 1 1,07 9,800. In addition to 

 the regular geologic and topographic work, the survey has now 

 in charge the reclamation of the arid lands. The ideas advanced 

 in 1877 by Major Powell, then Director of the Survey, regarding 

 the arid regions have at last been enacted into law. In the 

 matter of publications, great improvement is shown. Hereafter 

 the annual report will be confined to one volume and the matter 

 formerly contained in the unwieldy reports is to be published 

 as "professional papers." The work in Alaska is in charge of 

 four parties and is yielding results of great scientific and eco- 

 nomic value. (See Professional Papers, Nos. 1, 2, 10.) 



Professional Papers. No. 1. Preliminary Report on the 

 Ketchikan Mining District, Alaska; by A. H. 'Brooks, 120 pp., 

 2 pis., 6 figs. 



No. 2. Reconnaissance of the Northwestern Portion of Seward 

 Peninsula, Alaska; by A. J. Collier, 68 pp., 12 pis. 



No. 4. The Forests of Oregon; by Henry Gannett, 33 pp., 

 7 pis. 



