MERCURY VENUS THE EARTH. 



65 



spring, summer, autumn, and winter have once revolved. Owing to his near neighbour- 

 hood to the sun, his orb 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 with- 

 out 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 tempe- 

 rate 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. 



The mean distance of Mercury from the sun is thirty-seven millions of miles. His 

 period of revolution, and consequently his year, occupies 87 days, 23 hours and a 

 quarter, though his restless flight in space is prosecuted at the rate of more than a hun- 

 dred thousand miles an hour a speed which originated the name of the planet, from 

 the swift-winged messenger of the gods. His rotation upon his axis is accomplished in 

 rather more than twenty-four hours. His diameter is estimated to be 3140 miles. The 

 volume of Mercury must therefore be increased upwards of twenty millions of times in 

 order to equal the sun in magnitude ; but his mass, if increased only two millions of 

 times with matter of the same density, would equal him in weight. The planet 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 his greatest elongations. The telescope discovers phases like 

 the moon, and atmospheric indications. Some have even professed to discern irregu- 

 larities of outline, supposed to express superficial elevations ; but of this we have no 

 certainty. 



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 



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