306 THOMAS C. CHAMBERLIN 
nutation period as 432.8 days.’ This is so nearly commensurate 
with the fortnightly tide that there may be a resonance relation 
between them. The subnutation that has an annual period is 
probably the result of the seasonal shift of solar effects north and 
south of the equator. s 
7. The elastic nature-of the body tide is accepted as practicnlia 
demonstrated by the researches of Michelson, Gale, and Moulton, 
added to those of previous investigators.” 
8. The water tides are held to spring in part from the body 
tide and in part from the direct attraction of the tide-producing 
bodies; their rise to notable value depends on the resonance of their 
basins. 
THE TIME FACTOR 
g. The arguments once urged against any great age of the earth 
because of the sun’s short life, tidal action, etc., are held to be 
wholly invalid. An age somewhere between one billion and several 
billions of years seems best to fit in with astronomical and biological 
considerations. Ample time should be allowed for the evolution of 
star-clusters and the stellar galaxy, as well as life-evolution. 
10. Estimates of the earth’s age, based on current geological 
processes, require large corrections for the accelerating effects of 
present high reliefs and soil cultivation; in particular, for (qa) 
increased vertical circulation, (b) more rapid cycles of evaporation 
and precipitation, (c) greater instability of vegetal clothing, 
(d) more rapid run-off, (e) deeper penetration of solvent action, 
(f) greatly increased soil waste, and (g) the much greater length 
of the low-relief periods than of the high-relief periods. The 
required corrections are probably great enough to reconcile the 
geologic with the radioactive estimates. 
tr. For the computations used in the articles here summarized, 
a range wide enough to cover the uncorrected geologic as well as 
the radioactive estimates was used, as follows: (a) for the time since 
*W. Schweydar, Naturwissenschaften (1917), Potsdam, Germany, Part 38. 
2 A. A. Michelson and Henry G. Gale, ‘‘The Rigidity of the Earth,” Jour. Geol., 
Vol. XXVII (1919), pp. 585-601. 
3“‘The Quantitative Element in Circum-Continental Growth,” Article VIII, 
Jour. Geol., Vol. XXII (1914), pp. 516-28. 
