EDITORIAL 93 



elusion is based on the assumption that the thermal capacity 

 was 1.4 1. On the assumption that it was five thirds, which is the 

 largest permitted by the mechanical theory of heat, the conclu- 

 sion is reached that the contraction could at most have occupied 

 about 6,500,000 years. 



The foregoing computations are based upon Pouillet's estimate 

 of the present radiation of the sun. If the computation be based 

 on recent estimates, which give a rate at least 50 per cent, 

 greater, the resulting time is about 4,336,000 years. Ritter 

 recognizes that the departure of the body from a spherical shape 

 arising from rotation would modify the results, as these were 

 based on the assumption of a spherical form throughout the 

 whole period, but as this departure was large only during the 

 comparatively small portion of the whole interval occupied in 

 the contraction from the earth's orbit to twice the sun's present 

 diameter, the correction is limited, but yet may be consider- 

 able. In view of this the author remarks : " For these reasons 

 we cannot give the maximum value t = /\, 336, 000 years found 

 above the significance of a superior limit for the age of the 

 earth, the less in fact since the original assumptions must still 

 be regarded as hypotheses imperfectly satisfied. Nevertheless 

 it seems permissible to conclude from the above investigation 

 that the actual age of the earth must be far less than the esti- 

 mates of some geologists, who place it at hundreds of millions 

 of years." 



Whatever corrections may be applicable to such a computa- 

 tion, the attempt to subject the time factor of the gaseous 

 hypothesis of the evolution of the solar system to rigorous 

 mathematical inquiry is a most helpful one. The discussions 

 of Lord Kelvin and others who have attempted to assign limits 

 to the age of the earth by merely determining the maximum 

 amount of heat which the sun can have radiated in the past, on 

 the gravitational hypothesis, do not really get home to the ques- 

 tion, since they do not determine the rate of radiation of heat 

 in the past. If that rate were faster than the present rate it is 

 obvious that the time would be correspondingly shortened ; if 



