572 



SCIENCE 



[Vol. LV, No. 1430 



cliosen. If we denote it by c in any system of 

 units, we may formulate the law as follows: 



Two bodies attract one another inversely as 

 the square of their distance and directly as the 

 product of their masses and (1 + 3v-/c-), 

 where v is the component of their relative ve- 

 locity perpendicular to the line joining the 

 bodies. 



The form (1) is obtained from the Einstein 

 theory on the hypothesis that the planet is 

 small in comparison with the sun. It may be 

 that the above law applies only to this case. 

 However, it maj' be that the law would work 

 if the bodies were approximately of the same 

 mass. As fomiulated the law enables one to 

 set up the differential equations of n bodies in 

 a manner analogous to the classical theory. It 

 would be interesting to know whether known 

 discrepancies in the motion of the moon would 

 be overcome by the use of this law. 



Although the term 3v-/c- produces an ob- 

 servable effect only in the case of Mercury, it 

 may produce a signifieant effect in molecular 

 motion. 



4. When in like manner equation (7) is com- 

 pared with (9) we find that for a ray of light 

 the attraction is 

 (14) 3mto= 



where w may be interpreted as the angular 

 velocity of the light about the sun. Thus it is 

 the term 3mci)" in (13) which accounts for the 

 deflection of light, and the term m/r- does 

 not enter. Einstein and his followers have cal- 

 culated the deviation of light bj' noting that 

 the velocity changes in a manner analogous to 

 that of a refracting medium, and by applying 

 Huygen's principle. Since the same term ap- 

 pears in the attraction of a planet, it may 

 very well be that the sun affects the medium 

 through which both the light and planets pass, 

 and that the difference between Newton's law 

 and (13) is due to this situation. From this 

 point of view one would expect that the law 



1 1 have just found that A. T. Backlund in the 

 ArTciv for Matematik, Astronomioch Fysilc, Vols. 

 14 and 15 (just received) lias made an extensive 

 study of the relation between classical dynamics 

 and the Einstein theory of gravitation. In the 

 course of his three articles he obtains equation 

 (11) and one similar to (13). 



would not be accurate for two or more bodies 

 of relatively the same mass, but it may lead to 

 a sufficiently close approximation.^ 



Luther Pfahler Eisenhart 

 Princeton IjNrvERSiTT 



THE AMERICAN ASSOCIATION FOR 



THE ADVANCEMENT OF SCIENCE 



SECTION F— ZOOLOGICAL SCIENCES AND 



ASSOCIATED SOCIETIES 



At the Toronto meeting of the American 

 Association for the Advancement of Science, 

 December 27-31, 1921, Section F (Zoology) 

 oti'ered no separate program, but met jointly 

 with the American Society of Zoologists. The 

 program was arranged by the latter society. 



Six joint sessions were held, the program 

 including 101 titles distributed by subject as 

 follows: embryology, 4; cytology, 8; compara- 

 tive anatomy, 7; evolution and genetics, 24; 

 ecology and zoogeography (with the Ecological 

 Society of America), 13; general zoology, 2; 

 protozoology, 2; parasitology, 22; comparative 

 and general physiology, 17; unclassified, 2. 



The session of Friday afternoon, December 

 30, was devoted to a symposium on ortho- 

 genesis. A biologists' smoker was held Wednes- 

 day evening, December 28, and the zoologists' 

 dinner Friday evening, December 30. 



The business meeting of Section F took place 

 at the morning session on December 29, with 

 Vice-president Kofoid acting as chairman. 

 M. M. Metcalf is vice-president for Section F 

 for 1922. J. A. Detlefsen was elected a mem- 

 ber of the section committee for four years in 

 place of the retiring member, A. M. Reese. 



F. E. Lillie presented the following resolu- 

 tions drawn up by a conference of representa- 

 tives of the biological societies in regard to a 

 proposed federation of biological societies : 



Eesolved: 1. That it is the sense of this con- 

 ference that an inter-soeiety conference should be 

 called to study and report upon the feasibility 

 of federation of the biological societies and to 

 develop plans for the said federation. 



2. That for the purpose of effecting such an 

 organization, each society, and Sections F and G 

 of the American Association for the Advance- 

 ment of Science, be requested to designate its 

 president and secretary as members of an inter- 



