Mabch 10, 1911] 



SCIENCE 



381 



" Feldspar Aggregate Occurring in Nelson 

 County, Virginia," W. M. Thornton, Jr. 



" History of the Coconut Palm in America," 

 0. F. Cook. 



" New Mink from the Shell Heaps of Maine," 

 F. B. Loomis. 



The first mimber of the new journal, Phyto- 

 pathology, has just appeared. This periodical 

 is the official organ of the American Phyto- 

 pathological Society. It is to be published 

 bimonthly and to be devoted to both the purely 

 scientific and practical economic features of 

 plant disease investigations. The chief editors 

 are Dr. L. R. Jones, professor of plant pathol- 

 ogy. University of Wisconsin ; Dr. C. L. Shear, 

 plant pathologist, U. S. Department of Agri- 

 culture, and Professor H. H. Whetzel, pro- 

 fessor of plant pathology, Cornell University; 

 who are assisted by twelve associate editors, 

 representing different institutions and sec- 

 tions of the country. The initial number con- 

 tains 37 pages and 6 plates. An excellent por- 

 trait of Anton de Bary, hitherto unpublished, 

 appears in the frontispiece. The following 

 articles are included: 



"Anton de Bary" (with portrait), Erwin F. 

 Smith. 



" The Rusts of White and Red Clover," Frank 

 D. Kern. 



" Crown Gall of Plants," Erwin F. Smith. 



" Fig Diseases," C. W. Edgerton. 



" Floret Sterility of Wheats in the Southwest," 

 Edw. C. Johnson. 



" Black-ieg or Phoma Wilt of Cabbage," Thos. 

 F. Manns. 



" A New Fruit Spot of Apple," W. M. Scott. 



Reviews. 



SPECIAL ARTICLES 



A KINETIC THEOEY OF GRAVITATION' 



Ever since Sir Isaac Newton enunciated 

 the law of universal gravitation, more than 

 two hundred years ago, philosophers have 

 speculated on the nature of the mysterious 

 agency which links every atom of matter in 

 the universe with every other atom. Newton 

 was iinable to offer any adequate explanation. 



Since Newton's time several theories of 

 gravitation have been proposed, but all, of 



^ Read before the American Association for the 

 Advancement of Science, December, 1910. 



which I am aware, are open to strong objec- 

 tions and are not considered even promising 

 by physicists. 



Study of the nature of gravitation is beset 

 with unusual difficulties; because gravitation 

 is ever with us and about us, it is the one 

 universal phenomenon, and we can not escape 

 from its influence — can not obtain any out- 

 side point of view. 



Gravitation is often described as a feeble 

 force; and so it is, from one point of view. 

 It is difficult to measure, or even to detect, 

 attraction between two small bodies. But 

 when the bodies are of planetary size the ag- 

 gregate attraction of their molecules is enor- 

 mous. It is easy to calculate that the attrac- 

 tion between the earth and the moon, which 

 is just suflicient to retain the latter in its 

 orbit, would, if replaced by a steel cable, re- 

 quire that the cable be about five hundred 

 miles in diameter in order to withstand the 

 strain. Between the earth and sun, the cable 

 wo^ld have to be nearly as large in diameter 

 as the earth; and attraction between the com- 

 ponents of some double stars is millions of 

 times greater than between the earth and sun 

 (Lodge). So tremendous a phenomenon as 

 gravitation, a phenomenon compared with 

 which all others seem trivial, must have a 

 mighty origin. 



That gravitation is a phenomenon of the 

 all-pervading ether is beyond reasonable doubt. 

 This is so generally conceded that it need not 

 be argued. But how does the gravitative in- 

 fluence originate? how is it transmitted and 

 maintained? what is the mechanism of gravi- 

 tation? It is the purpose of this paper to 

 attempt an answer to these questions. 



Let us consider what happens to a falling 

 body. We know that it gathers kinetic energy 

 from some source, as evidenced by its accel- 

 eration; that this energy may do external 

 work or develop heat; that the amount of 

 energy gathered is measured directly by the 

 distance fallen through (within the limits of 

 uniform gravitation), irrespective of the time 

 or rate of falling. When the distance fallen 

 through is of inter-planetary magnitude, and 

 the attracting body large, the gathered energy 



