Acting on a very old tradition, some people from Salisbury and other surrounding places go to observe the sunrise on the longest day of the year at Stonehenge. We therefore are perfectly justified in assuming that it was a solar temple used for observation in the height of midsummer. But at dawn in midsummer in these latitudes the sky is so bright that it is not easy to see stars even if we get up in the morning to look for them; stars, therefore, were not in question, so that some other principle had to be adopted, and that was to point the temple directly to the position on the horizon at which the sun rose on that particular day of the year, and no other. Now, if there were no change in the position of the sun, that, of course, would go on for ever and ever; but, fortunately for archæologists, there is a slight change in the position of the sun, as there is in the case of a star, but for a different reason; the planes of the ecliptic and of the equator undergo a slight change in the angle included between them. So far as we know, that angle has been gradually getting less for many thousands of years, so that, in the case of Stonehenge, if we wish to determine the date, having no stars to help us, the only thing that we can hope to get any information from is the very slow change of this angle; that, therefore, was the special point which Mr. Penrose and I were anxious to study at Stonehenge, for the reason that we seemed in a position to do it there more conveniently than anywhere else in Britain. [Illustration: FIG. 8.--The original tooling of the stone protected from the action of the weather.] But while the astronomical conditions are better at Stonehenge than elsewhere, the ruined state of the monument makes accurate measurements very difficult. Great age and the action of weather are responsible for much havoc, so that very many of the stones are now recumbent, as will be gathered from an article by Mr. Lewis, who described the condition of the monument in 1901, in _Man_. [Illustration: FIG. 9.--View of Stonehenge from the west. A, stone which fell in 1900; _BB_, stones which fell in 1797. (Reproduced from an article on the fallen stones by Mr. Lewis in _Man_.)] Professor Gowland in his excavations at Stonehenge, to which I shall refer in the sequel, found the original tooled surface near the bottom of one of the large sarsens which had been protected from the action of the weather by having been buried in the ground. It enables us to imagine the appearance of the monument as it left the hands of the builders (Fig. 8). [Illustration: FIG. 10.--Copy of Hoare’s plan of 1810, showing the unbroken Vallum and its relation with the Avenue.]