Views of Mercury, however, such as they are, are by no means so difficult to secure as is sometimes supposed. Denning remarks that he has seen the planet on about sixty-five occasions with the naked eye--that in May, 1876, he saw it on thirteen different evenings, and on ten occasions between April 22 and May 11, 1890; and he states it as his opinion that anyone who will make it a practice to obtain naked-eye views should succeed from about twelve to fifteen times in the year. During the spring of 1905, to take a recent example, Mercury was quite a conspicuous object for some time in the Western sky, close to the horizon, and there was no difficulty whatever in obtaining several views of him both with the telescope and with the naked eye, though the disc was too much disturbed by atmospheric tremors for anything to be made of it telescopically. In his little book, 'Half-hours with the Telescope,' Proctor gives a method of finding the planet which would no doubt prove quite satisfactory in practice, but is somewhat needlessly elaborate. Anyone who takes the pains to note those dates when Mercury is most favourably placed for observation--dates easily ascertained from Whitaker or any other good almanac--and to carefully scan the sky near the horizon after sunset either with the naked eye, or, better, with a good binocular, will scarcely fail to detect the little planet which an old English writer more graphically than gracefully calls 'a squinting lacquey of the sun.' Mercury is about 3,000 miles in diameter, and circles round the sun at a mean distance of 36,000,000 miles. His orbit is very eccentric, so that when nearest to the sun this distance is reduced to 28,500,000, while when furthest away from him it rises to 43,500,000. The proportion of sunlight which falls upon the planet must therefore vary considerably at different points of his orbit. In fact, when he is nearest to the sun he receives nine times as much light and heat as would be received by an equal area of the earth; but when the conditions are reversed, only four times the same amount. The bulk of the planet is about one-nineteenth that of the earth, but its weight is only one-thirtieth, so that its materials are proportionately less dense than those of our own globe. It is about 3-1/2 times as dense as water, the corresponding figure for the earth being rather more than 5-1/2.