AND THEORY OF THE HEAVENS. 91 



tage over Mars by its distance, has not been completely 

 freed from suffering a considerable loss through Jupiter's 

 attraction. And it seems to me that Mercury owes 

 the exceptional smallness of its mass not only to 

 the attraction of the mighty sun being so near it, but 

 also to the neighbourhood of Venus, which, if we com- 

 pare its probable density with its magnitude, must be a 

 planet of considerable mass. 



Everything concurs as admirably as could be desired, 

 in corroborating the sufficiency of a mechanical theory 

 as an explanation of the origin of the construction of the 

 world and of the heavenly bodies. Taking into account 

 the space in which the constituent matter of the planets 

 was scattered before their formation, we shall now pro- 

 ceed to consider what was the degree of tenuity of the 

 matter which filled this intervening space, and with what 

 sort of freedom and with how few obstructions the floating 

 particles may have started on their regulated movements 

 therein. If the space which held all the matter of the 

 planets within it, was contained in that portion of the 

 sphere of Saturn which is contained between two planes 

 at an angle of between 2 degrees and 7 degrees and 

 extending from the centre of the sun to all distances, 

 and was therefore the seventeenth part of the whole 

 sphere which can be described with the radius of the 

 distance of Saturn ; and if, in order to calculate the 

 alteration of the primitive planetary matter when it filled 

 this space, we take the distance of Saturn to be only 

 100,000 diameters of the earth : then the whole sphere 

 of the orbit of Saturn would exceed in volume that of 

 the earth 1000 bimillion times. And if instead of the 

 seventeenth part we take only the twentieth of this 



