The most obvious peculiarity of this planet--its polar snow-caps--were seen about 250 years ago, but they were first proved to increase and decrease alternately, in the summer and winter of each hemisphere, by Sir William Herschell in the latter part of the eighteenth century.

This fact gave the impulse to that idea of similarity in the conditions of Mars and the earth, which the recognition of many large dusky patches and streaks as water, and the more ruddy and brighter portions as land, further increased.

Added to this, a day only about half an hour longer than our own, and a succession of seasons of the same character as ours but of nearly double the length owing to its much longer year, seemed to leave little wanting to render this planet a true earth on a smaller scale.

It was therefore very natural to suppose that it must be inhabited, and that we should some day obtain evidence of the fact.
_The Canals discovered by Schiaparelli._ Hence the great interest excited when Schiaparelli, at the Milan Observatory, during the very favourable opposition of 1877 and 1879, observed that the whole of the tropical and temperate regions from 60 deg.
N.to 60 deg.

S.Lat.were covered with a remarkable network of broader curved and narrower straight lines of a dark colour.