GEOLOGY. 383 



9. A study of the aberrant features of the solar system seemed to 

 bring them into harmonious genetic and working relations with the 

 normal features and, so interpreted, they give concurrent and confirma- 

 tory testimony. 



10. The explosive vulcanism of the moon and also that of the earth 

 furnish cogent reasons for replacing the inherited view that they were 

 once molten globes by an accretional origin better adapted to furnish 

 the essential conditions of explosive action. 



11. The convergent testimony of recent observational, experi- 

 mental, and mathematical investigations on the behavior of rock 

 under stress, on the body tides, on the polar nutation, and on the 

 transmission of seismic waves, points to an increase of density, rigidity, 

 and elasticity graded toward the earth's center in harmony with the 

 natural effects of oscillating stress differences which grow more mtense 

 in a similar ratio from surface to center. To bring the whole into 

 harmony, the high mean values of all these increasing physical 

 properties require a consistent extension of the gradation over the 

 ground not yet covered by explicit observation. The conclusions 

 reached by the comparison of the earth with its neighbors and the 

 collateral inquiry into the fomiative processes give results that are in 

 close accord with the convergent determinations of the several other 

 lines of investigation that are now beginning to throw revolutionary 

 light on the constitution of the earth. 



HISTORY. 



Fox, Dixon R., Columbia University, New York, N. Y. Cotnpletion of the 

 work of the late Professor- H. L. Osgood toward an institutional history of the 

 American Colonies during the period of the French wars. (For previous 

 reports see Year Books Nos. 11-18.) 



Much progress has been made in revising and completing the manu- 

 script of the late Professor Herbert L. Osgood on "The American 

 Colonies in the Eighteenth Century,' ' which will be ready for publi- 

 cation in four volumes about November 1920. Inasmuch as my own 

 work is critical and supplementary, rather than extensively original, 

 no further report here seems necessary. These volumes, continuing 

 the three published in 1904 and 1907, will be in themselves a report of 

 a Ufe-work in the origins of American institutions. Professor Frank 

 W. Pitman, of Yale University, will contribute a chapter on the 

 "West Indies in the Eighteenth Century." 



HISTORY OF SCIENCE. 



Sarton, George, Cambridge, Massachusetts. Associate in the History of 

 Science. (For previous report see Year Book No. 18.) 



The general purpose of my efforts was explained in my first 

 report (Year Book No. 18, pp. 347-349). The present report deals 

 with the period extending from July 1919 to the end of August 1920. 



