SECT.V.] ECLIPSES OF PLANETS. 47 



centre of the earth, and of the moon from her node at the 

 instant of conjunction, occasions great varieties in the solar 

 eclipses. Besides, the height of the moon above the horizon 

 changes her apparent diameter, and may augment or di- 

 minish the apparent distances of the centres of the sun and 

 moon, so that an eclipse of the sun may occur to the inha- 

 bitants of one country, and not to those of another. In this 

 respect the solar eclipses differ from the lunar, which are the 

 same for every part of the earth where the moon is above 

 the horizon. In solar eclipses, the light reflected by the at- 

 mosphere diminishes the obscurity they produce. Even in 

 total eclipses the higher part of the atmosphere is enlight- 

 ened by a part of the sun's disc, and reflects its rays to the 

 earth. The whole disc of the new moon is frequently visible 

 from atmospheric reflection. 



A phenomenon altogether unprecedented occurred during 

 the total eclipse of the sun which happened on the 8th of 

 July, 1842. The moon was like a black patch on the sky, 

 surrounded by a faint whitish light about the eighth of the 

 moon's diameter in breadth, in which three red flames ap_ 

 peared in form like the teeth of a saw; from what cause 

 they originated, or what they were, is totally unknown. 



Planets sometimes eclipse one another. On the 17th of 

 May, 1737, Mercury was eclipsed by Venus near their in- 

 ferior conjunction ; Mars passed over Jupiter on the 9th of 

 January, 1591 ; and on the 30th of October, 1825, the moon 

 eclipsed Saturn. These phenomena, however, happen very 

 seldom, because all the planets, or even a part of them, are 

 very rarely seen in conjunction at once ; that is, in the same 

 part of the heavens at the same time. More than 2500 years 

 before our era, the five great planets were in conjunction. 

 On the 15th of September, 1186, a similar assemblage took 

 place between the constellations of Virgo and Libra; and, in 

 1801, the Moon, Jupiter, Saturn, and Venus were united in 

 the heart of the Lion. These conjunctions are so rare, that 

 Lalande has computed that more than seventeen millions of 



