ASTRONOMY AND METEOROLOGY. 371 



longitudes of Uranus, 'that the disturbing action of an unknown planet 

 (Neptune) was ascertained, and, by marvellous refinements of cal- 

 culation, its very place in the heavens pointed out. 



Entering into a comparison of the results afforded by the separate 

 study of each one of the planets, M. Leverrier finds that the position 

 and small size of Mercury and Mars prevent them from exercising 

 any important influence upon the bodies of our system. Observa- 

 tions upon Venus enable us to estimate the mass of Mercury as one 

 five-millionth (^i-^-g.) of that of the sun ; while the motion of the 

 earth, deduced from observations of the sun, indicates the mass of 

 Mars as one three-millionth (3000000) *kat ^ tue sun - The un- 

 certainty which may exist in these numbers has no influence upon 

 that which follows. 



The mass of Venus is not far from one four-hundred-thousandth 

 (700*000) tna t f * ne sun - ^he result is obtained by several meth- 

 ods : by the consideration of the displacement of the plane of the 

 ecliptic ; by the actual measurement of the periodical perturbations 

 of the earth from 1750 to 1810, and from 1811 to 1850; and by the 

 amount of the periodical inequalities of the longitude of Mercury. 

 These results all confirm each other. 



The mass of the earth is one three-himdred-and-fifty-fi ve-thousandth 

 (3 5 '5*0 oo") f that of the sun. This number is derived from a com- 

 parison of the force of gravity upon the earth, with the fall of our 

 own planet toward the sun. 



Setting out from these data, the French astronomer finds that, to 

 reconcile the ancient with the modern observations of Mars, it is 

 necessary to accelerate his perihelion movement. To find an ade- 

 quate cause for this, again, we must assume an increase in the attrac- 

 tive force of the earth or Venus, that is, in the computed mass of one 

 or both of these planets. But the action of Venus on Mars is, from 

 its position, comparatively feeble ; and the value of its mass rests on 

 grounds that are considered unassailable. We have no alternative, 

 then, but to add to the computed mass of the earth, and an addition 

 of a tenth suffices. But there are good reasons against admitting 

 such a change ; and an equal quantity of matter, in another form, re- 

 volving round the sun at the same distance, will give us the attractive 

 force required. 



As already remarked, the study of the inequalities of Mercury led 

 Leverrier, in 1859, to the inference that a ring of masses of matter 

 existed within the orbit of Mercury, or between it and the sun. His 

 reasons for believing that the disturbing cause in the case of Mercury 

 was a ring of small masses of matter, rather than one large body, 

 were, that a single planet comparable to Mercury, as regards its di- 

 mensions, and revolving within its orbit, could not have escaped the 

 recognition of astronomers, especially during the total eclipses of the 

 sun. On the other hand, says Leverrier, if the cosmical disturbing- 

 matter has such a disposition, that, although partly or wholly invisi- 

 ble, it acts in such a manner as to increase the direct motion of the 

 perihelion, having but little influence apart from this, it is easy to see 

 how the existence of matter in this connection becomes highly proba- 

 ble. This, in fact, is the mode of action of a series of small bodies 

 forming a ring about the sun, and revolving from west to east, in the 



