152 ANNUAL KEPOKT SMITHSONIAN INSTITUTION, 1925 



MASS AND VP:L0CITY 



A statistical study of the masses and the velocities of stars revealed 

 a striking correlation, which though incomplete pointed toward 

 equipartition of Qncrgy. No satisfactory explanation of this was 

 offered until Jeans dispelled the clouds of mystery by showing that 

 it is essentially the same problem as that just discussed. The mutual 

 influences of tlie stars, originally sixty-four times as closely packed 

 as now, have resulted in the course of 10'- 3'ears in bringing some 

 measure of order out of i)riiiic\al disorder. It is analogous to the 

 behavior of a mixture of gases -if undisturbed by external influences 

 the tendenc}' would be for (hose molecules most massive to move most 

 slowly while the lighter molecules moved with the greater speed, the 

 kinetic energy or product of mass by velocity squared, tending to be 

 the same for all the molecules. This also formed a basis, though 

 of a tiuth a somewhat shaky basis, for again confirming the age of 

 the galaxy as 10^^ years. 



SOLAR SYSTEMS 



Tlie nebular hypothesis of Laplace and the planetesimal hypothesis 

 of Chamberlin have gone into the history of science as great and 

 lasting monuments to their originators, both of whom were powerful 

 and constructive thinkers. As a direct development from Chamber- 

 lin 's hypothesis, Jeans some years ago worked out upon a rigorous 

 mathematical basis his tidal theory of the origin of the solar system. 

 In view of the contrast between his conclusions in 1919 and his 

 present conclusions in the light of the researches under review, it is 

 worth while to consider the tidal theor}^ in some detail. 



An analysis of the equilibrium forms of rotating fluids under 

 various conditions amenable to mathematical treatment, revealed the 

 fact that within a rotating gaseous mass there are no forces which 

 could combine to produce a series of j^lanets such as encircle our sun. 

 Hence, following the lead of Chamberlin, Jeans called in the aid of 

 a passing star to suppl}^ the force necessary to disrupt the parent 

 sun. It is obvious that a close approach of one star to another would 

 draAV out tides, one on each side of the star considered, the tidal arm 

 on the side nearest to the tide-producing star being slightly the 

 greater, and therefore more readily drawn out to a distance produc- 

 ing its instability. The mattei" in this arm would then break away 

 from the parent sun and follow orbits about the sun in directions 

 governed by the direction of travel of the passing star. Condensa- 

 tion would gradually take place about any points in the tidal arm 

 where there happened to be a local concentration of gas. Each of 

 these nuclei would become one of the planets, and its orbit and other 

 individual characteristics Avould be determined, in part at least, by 



