404 THE WORLD MACHINE 



500 satellites and two new planets added, it is still less than 

 a 75oth. The quantity is very small. If a 75oth part were 

 chipped off a cannon-ball or a melon, neither would greatly 

 suffer. The trained imagination of the investigator of nature 

 swept swiftly to the thought perhaps here is the explanation. 



Buffon put with this Newtonian computation another of 

 his own. Knowing the distance of the planets and their ap- 

 parent diameters, it is a simple enough matter to calculate 

 their volume ; that of the sun as well. The volume divided 

 by the mass is the measure of density that is to say, the unit 

 quantity of matter in a chosen unit of space. According to 

 Buffon's calculation the average density of the planets is to 

 that of the sun as 640 to 650 ; in a word, the relation was 

 very near to unity. But if the stuff of the planets is of the 

 same density as that of the sun, then it is next to certain that 

 it is the same stuff. The figures were in error ; but the con- 

 clusion was true. Remember that this was more than 150 years 

 ago, a long time before the development of chemistry, a century 

 almost before the use of the spectroscope ; it was an intuition 

 of genius. 



With this discovery there seemed little question, then, that 

 our little earth and all its kind were once a part of the sun. 

 Somewise or other these planetary bits had been thrown off, 

 brushed off, from the glowing mass, had cooled down into 

 solid orbs and taken up their common way around the parent 

 sun. It was a splendid guess but how had it come ? 



There were dozens of ways, of course. There might be vast 

 eruptions upon the sun like those upon the earth which had 

 destroyed Pompeii. There might be colossal explosions like 

 that which in our own time blew away the island of Krakatoa. 

 Buffon thought of another. Up to this time he had been 

 following the firm path of induction, now he struck off into 

 analogy and guesswork. The study of comets, the plotting 

 of their orbits, the prediction of their return, was the order 

 of the day. Some of them were very vast they moved at 

 frightful speed. Newton had shown that some of them smash 

 into the sun, some just graze its edge. It was known that some 

 of them at least come probably from beyond the confines of our 

 planetary system. Was it not conceivable that from some- 

 where in the distant ways there had come one of especial power 

 and great bulk, rushing along with such impetus as to cut 



