CONDITION OF THE LARGER PLANETS. 185 



as much heat ; but he would have about 340 times as 

 much heat to part with for each degree of cooling ; 

 hence his rate of cooling would be slower in the propor- 

 tion of about 7 to 1. Jupiter appears actually to have 

 a much greater volume than has been here supposed, 

 liis diameter exceeding that of the earth nearly eleven 

 times and his surface exceeding hers about 115 times. 

 This would still leave his rate of cooling slower in the 

 proportion of about three to one. But inasmuch as it 

 is certain that if formed of the same material, Jupiter, 

 when at the same stage of cooling, would be much 

 denser than the earth (because of his greater attractive 

 energy), our assumption rather falls short of the truth 

 than exceeds it. The argument next to be considered 

 will sufficiently indicate this. To complete the present 

 argument it is only necessary to add that the various 

 stages of cooling through which our earth has already 

 passed have certainly required hundreds of millions of 

 years, wherefore the corresponding stages for Jupiter 

 would require seven times as many hundreds, and the 

 total period required by Jupiter to reach the earth's 

 present condition of development would exceed the 

 time during which our earth has endured, from her 

 beginning until now, six times, even though Jupiter 

 at his beginning were no hotter than the earth. As he 

 was certainly much hotter, it may fairly be said that 

 he would require thousands of millions of years to reach 

 the stage which the earth has reached after hundreds 

 of millions of years ; and that, if the two planets were 

 both fashioned at the same time, Jupiter must^ still 



