MASSES OF THE PLANETS. 



SECTION VIII. 



Masses of Planets that have no Satellites determined from their Perturbations 

 Masses of the others obtained from the Motions of their Satellites Masses 

 of the Sun, the Earth, of Jupiter and of the Jovial System Mass of the 

 Moon Real Diameters of Planets, how obtained Size of Sun, Densities 

 of the Heavenly Bodies Formation of Astronomical Tables Requisite Data 

 and Means of obtaining them. 



THE masses of such planets as have no satellites are known 

 by comparing the inequalities they produce in the motions 

 of the earth and of each other, determined theoretically, 

 with the same inequalities given by observation ; for the 

 disturbing cause must neccessarily be proportional to the 

 effect it produces. The massesof the satellites themselves 

 may also be compared with that of the sun by their pertur- 

 bations. Thus, it is found, from the comparison of a vast 

 number of observations, with La Place's theory of Jupiter's 

 satellites, that the mass of the sun is no less than 65,000,000 

 times greater than the least of these moons. But, as the 

 quantities of matter in any two primary planets are directly 

 as the cubes of the mean distances at which their satellites 

 revolve, and inversely as the squares of their periodic times 

 (N. 133), the mass of the sun and of any planets which have 

 satellites may be compared with the mass of the earth. In 

 this manner it is computed that the mass of the sun is 

 354,936 times that of the earth ; whence the great pertur- 

 bations of the moon, and the rapid motion of the perigee and 

 nodes of her orbit (N. 134). Even Jupiter, the largest of 

 the planets, has recently been found by Professor Airy to 

 be 10487 times less than the sun ; and, indeed, the mass of 

 the whole Jovial System is not more than the 1046'77th part 



