58 



Marvels of the Universe 



But a world eternal!}^ covered in frost, snow or ice should sparkle under the sun's rays like a 

 diamond, and Mars is the " ruddy " planet and has as poor a power of reflection as the Moon. Is it 

 possible, then, that Mars is destitute of water, and is simply, like the Moon, naked rock ? No. for as 

 the accompanying illustrations show, a white cap crowns each of the poles of IMars ; a cap so 

 brilhant that it has been seen in the telescope to shine like a star of the first magnitude when a 

 mist or fog has entirely hidden the body of the planet. And this cap, like snow upon the earth, 

 increases in area as winter draws on, and diminishes with the approach of summer. Such changes 

 are impossible to bare rock ; it is but reasonable to ascribe them to ice or snow. For as the 

 white cap that is feeling the summer sun shrinks, so the region round it becomes dark, as if the 

 snow had indeed been melted and become turbid water. 



But the ice-caps of Mars are not relatively more extended than those of the earth, even in winter- 



ISO 190 SOO 310 





Phifelhontla Ele 



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EF'i THR^UM 











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THE MOST COMPLETE CHART OF THE PLANET MARS. 



This map was drawn by M. Antoniadi. and is based upon most recent discoveries. It is supposed that the dark parts of the 

 planet formed the seas in ages gone by. as their names signify (vide. Mare Sirenum Mare Acidalum, etc.). The narrow lines 

 connecting the darker spots are the much-discussed canals, accepted as such by some astronomers and rejected by others. The 

 former suggest that the darkness of the lines is caused by vegetation which clusters round the darker spots, or Luci," as they 

 are technically called. 



time, and in the summer they shrink and shrink, until in some years one of them has been known to 

 disappear entirely. Is not t-his evidence that Mars is warmer, not colder, than the earth ? 



This might be so, if we saw every part of the planet to the same advantage. But the Mars that 

 we examine in the telescope is not the average Mars. The little planet, true to his warrior reputation, 

 puts the best face on things ; we see him only under his happiest conditions ; he presents to us most 

 fuUy the summer noonday of his tropics, and hides from us " the winter of his discontent." 



The mean temperature of the earth is taken as 6o°, but the mean noontide temperature of our 

 tropics in summer-time wiU probably turn ioo°. A similar difference would, therefore, give us 

 50° as the average temperature of the centre of the disc of Mars as we see it. We need to know 

 not only the mean temperature of the planet, but the range of temperature, the range from midday 

 to midnight, the range from midsummer to midwinter, the range from equator to the poles. 



And this must be very great — greater than we experience under similar conditions here. We 

 infer this from what has been ascertained as to the force of gravity at the surface of Mars. This we 

 know to be about three-eighths that of the earth ; so that whilst a bodv falls sixteen feet in a second 



