The Red Planet is our nearest neighbour on the further, as Venus is on the hither side. He is also in some ways the planet best situated for our observation; for while the greatest apparent diameter of his disc is considerably less than that of Venus, he does not hide close to the sun's rays like the inferior planets, but may be seen all night when in opposition.[*] Not all oppositions, however, are equally favourable. Under the best circumstances he may come as near to us as 35,000,000 miles; when less favourably situated, he may come no nearer than 61,000,000. This very considerable variation in his distance arises from the eccentricity of the planet's orbit, which amounts to nearly one-tenth, and, so far as we are concerned, it means that his disc is three times larger when he comes to opposition at his least distance from the sun than it is when the conditions are reversed. Under the most favourable circumstances--_i.e._, when opposition and perihelion[†] occur together, he presents, it has been calculated, a disc of the same diameter as a half sovereign held up 2,000 yards from the spectator. Periods of opposition recur at intervals of about 780 days, and at the more favourable ones the planet's brilliancy is very striking. The 1877 opposition was very notable in this respect, and in others connected with the study of Mars, and that which preceded the Crimean War was also marked by great brilliancy. Readers of Tennyson will remember how Maud 'Seem'd to divide in a dream from a band of the blest, And spoke of a hope for the world in the coming wars-- ... and pointed to Mars As he glow'd like a ruddy shield on the Lion's breast.' Ancient records tell us of his brightness having been so great on some occasions as to create a panic. Panics were evidently more easily created by celestial phenomena then than they are now; but possibly such statements have to be taken with a small grain of salt. The diameter of Mars is 4,200 miles. In volume he is equal to one-seventh of the world; but his density is somewhat smaller, so that nine globes such as Mars would be required to balance the earth. He turns upon his axis in twenty-four hours thirty-seven minutes, and as the inclination of the axis is not much different from that of our own world he will experience seasonal effects somewhat similar to the changes of our own seasons. The Martian seasons, however, will be considerably longer than ours, as the year of Mars occupies 687 days, and they will be further modified by the large variation which his distance from the sun undergoes in the course of his year--the difference between his greatest and least distances being no less than 26,500,000 miles.