io FORMATION OF THE EARTH 



seems to be confirmed by the position occupied by the ring of 

 asteroids. In fact, the distance of the different planets from the 

 sun is controlled by a law formulated by the astronomer Bode, 

 of Berlin, which may be set forth as follows, if we take as the 

 point of departure not the sun but the last of the planets to 

 be formed, Mercury : — 



The distances of the planets from Mercury form a geometrical 

 progression whose first term is 3 and ratio 2. 



That is to say, the distances are to one another as the 

 following numbers :— 



Venus Earth Mars Jupiter Saturn. 



3 3x2 = 6 6x2 = 12 12x2= 24 24x2=48 48x2 = 96 



This law, first established by observation, was rediscovered in 

 1867 through computation. As the astronomer Heinrichs has 

 shown, it is due to the progressive condensation, regular and 

 proportional to time, of the solar nebula, and is of such a nature 

 that it also links together both the distances of the planets from 

 the sun and the epochs of their formation. Now, in this series 

 the planet corresponding to the number 24 is represented by 

 the ring of asteroids. This ring therefore corresponds to a 

 planet. It is also possible that the asteroids are not the result 

 of the rupture of a planet but of a ring which once encircled 

 the sun as Saturn is encircled to-day. 



Although the various planets are only formed of substances 

 found on the earth, it does not necessarily follow that each 

 one contains all of them, still less that it contains them all in 

 the same proportions. Their differences in density even force 

 us to assume, that this could not be the case. If, for instance, 

 we take water as the unit of density, we find that of Neptune 

 to be 17, that of Uranus i'5, and that of Jupiter 1*3. These 

 densities are only slightly higher than that of water, scarcely 

 equal to that of sugar, and much lower than that of glass. 

 Saturn, indeed, is so light that if there were a basin large 

 enough to hold it, it would float on the water. The density 

 of Mars on the other hand is 3*9, that of the Earth 5*5, Venus 

 4'4, and Mercury 6'5. These four planets may contain more or 

 less of the heavy metals, and may have a more or less extensive 

 atmosphere ; but their densities approximate too closely for 

 us not to assume that the same simple elements would be found 

 there. The lightness of the planets outside the ring implies a 



