Page:In the high heavens.djvu/128

 most world-like of all the other globes which come within the range of effective observation. It would, indeed, be very rash to assert that other bodies may not have a closer resemblance to our earth than Mars has, but of them we have either little knowledge, as in the case of Venus, or no knowledge at all. No doubt both Jupiter and Saturn can vie with Mars in the copiousness of detail with which they delight the astronomers who study them. These grand planets are deserving of every attention, but then the interest they excite is of a wholly different kind from that which makes a view of Mars so attractive. Jupiter offers us a meteorological study of the most astounding cloud-system in creation. Saturn gives an illustration of a marvellous dynamical-system the like of which would never have been thought possible had it not actually presented itself to our notice. But the significance of Mars is essentially derived from those points of resemblance to the earth which are now engrossing attention. Mars is clearly a possible world, presenting both remarkable analogies and remarkable contrasts to our own world, and inducing us to put forth our utmost endeavours to utilise so exceptional an occasion as that presented in the close approach which it made in 1892. Let us see what we have learned about this globe.

In the first place, it should be noticed that Mars must be a small world in comparison with our own. The width of this globe is only 4,200 miles, so that its volume is but the seventh part of that of the earth. The weight of Mars is even less than what might have been expected from his bulk. It would take nearly ten globes, each as heavy as Mars, to form a weight equal to that of the earth. This fundamental difference in dimensions