MERCURY VENUS THE EARTH. 



65 



spring, summer, autumn, and winter have once revolved. Owing to comparatively near 

 neighbourhood, the sun will occupy seven times more space in the Mercurian heavens than 

 in ours, and afford a light and heat which would be intolerable to our organs without some 

 modifying circumstances. We may, however, dismiss the idea of water always boiling at 

 the surface, and an ever-burning heat seven times greater than the fiercest experienced at 

 our equator, distinguishing its material. The sensible heat at the different planets may 

 depend chiefly upon their substance being more or less adapted to combine with the solar 

 influence ; there is nothing improbable, therefore, in the supposition that the nearest may 

 be as cool, and the remotest as warm, as the temperate zones of the earth. Besides, it is 

 a proud presumption to imagine the organism of the terrestrials to be the standard and 

 model of finite beings. We are bound to admit that the great Author of existence can 

 as duly attemper to every dwelling-place the physical constitution of its inhabitants, as 

 obtains with reference to our globe and its population. 



Mercury is at the mean distance of thirty-seven millions of miles from the sun, and 

 performs an orbital revolution in about 88 days, travelling at the rate of more than a 

 hundred thousand miles an hour. This speed originated the name that of the swift- 

 winged messenger of the gods. The planet rotates upon its axis in rather more than 

 twenty-four hours, and has a diameter of 2950 miles. Its volume must therefore be 

 increased upwards of twenty millions of times in order to equal the sun in magnitude ; 

 but the mass, if increased only two millions of times with matter of the same density, 

 would be equal in weight. Mercury is an evening star when eastward of the sun, and a 

 morning star when westward of him, but is quite invisible to the naked eye, owing to the 

 vicinity of the solar splendour, except at or near the time of the greatest elongations. The 

 telescope discovers phases like the moon, and atmospheric indications. Some have even 

 professed to discern irregularities of outline, supposed to express superficial elevations ; 

 but of this we have no certainty. Not the least departure from the circular form 

 in the shape of the planet was detected till the transit of November 1848, when 

 micrometrical measurements, executed by the Eev. Mr Dawes, showed it to be slightly 

 spheroidal. 



Astronomers have been sorely plagued in their observation of Mercury a giddy planet 

 imperceptible generally, through a close attendance upon the sun never at such a 

 distance from him as to appear in a dark part of the heavens and going at a rate 

 through space, which is a perfect gallop when compared with the sober jog-trot of the 

 earth. These circumstances, together with the smallness of the planet's mass, and a 



peculiar quick scintillation, render it a very 

 difficult object to examine. Copernicus is said 

 never to have seen Mercury through his whole 

 life, and Delambre was only able to discern him 

 twice with the naked eye. The description of 

 one of the old writers a "squirting lacquey 

 of the sun, who seldom shows his head in these 

 parts, as if he were in debt" however odd, is 

 yet characteristic. The planet may be caught 

 for a short time before sunrise in autumn, and 

 after sunset in spring ; and appears to shine 

 with a brilliant white light, being alternately 

 a crescent, a semicircle, and gibbous. When 

 between us and the sun, and at the same time 

 in the plane of the earth's orbit, Mercury transits 

 the solar disk, and is seen as a small black speck 



