MARS, A WORLD MORE ADVANCED THAN OURS Mars is the fourth planet in the order of distance from the sun, and the outermost member of the terrestrial group.

Its mean distance is 141,500,000 miles, variable, through the eccentricity of its orbit, to the extent of about 13,000,000 miles.

It will be observed that this is only a million miles less than the variation in Mercury's distance from the sun, from which, in a previous chapter, were deduced most momentous consequences; but, in the case of Mars, the ratio of the variation to the mean distance is far smaller than with Mercury, so that the effect upon the temperature of the planet is relatively insignificant.
Mars gets a little less than half as much solar light and heat as the earth receives, its situation in this respect being just the opposite to that of Venus.

Its period of orbital revolution, or the length of its year, is 687 of our days.

The diameter of Mars is 4,200 miles, and its density is 73 per cent of the earth's density.