Janssen, the French astronomer, who died about the same time as Lord Kelvin, acquired celebrity by his discovery of a method for seeing and studying the great flames or prominences which surround the sun. The glare of the great fiery ball is such that the eye is blinded in ordinary circumstances to the light of these prominences. They were only known from their coming into view during the total eclipse of the sun’s disc by the moon. Then they were seen as a great fringe of pointed, tongue-like flames around the darkened disc. But at other times no use of smoked glass or telescope could bring them into view. Janssen went to India in 1868 to study these prominences of the sun during the total eclipse of that year. His purpose was to examine with a spectroscope the light given out by the prominences. The day after the eclipse Janssen found that he could still examine the prominences and make out their shape and the chemical elements present in them by looking at them through the spectroscope, although the sun’s disc was now uncovered, and it was impossible to see the prominences with the unaided eye or with the telescope.

A young English astronomer, hundreds of miles apart from Janssen, on the same day, Aug. 18, 1868, made the same discovery in the same way, independently. The English astronomer was Norman Lockyer, and the French Academy of Sciences caused a medal to be struck in commemoration of this discovery. The medal is before me as I write. It shows the heads of Janssen and of Lockyer side by side, as they were forty years ago.

Each has carried on his researches and discoveries with unabated vigour since that happy conjunction. Sir Norman Lockyer has for many years added to his constant study of the sun, fixed stars, and nebulÆ by means of the spectroscope and photographic record of spectra, an inquiry into the evidence afforded by astronomical facts first as to the age of Greek and Egyptian temples, and latterly as to that of the mysterious avenues and circles of stones (such as Stonehenge) scattered about the British Islands, of the history and use of which we have only vague traditions and no actual records. These stone circles and avenues are very numerous in Great Britain. The chief are Stonehenge, Avebury, and Stanton Drew in the middle South of England; the Hurlers, Boscawen-Un, Tregaseal, the Merry Maidens, and the Nine Maidens in Cornwall; Merrivale Avenue and Fernworthy Avenue in Devon; many circles in Aberdeenshire, in Cumberland, Derbyshire, and Oxfordshire, as well as monuments of the same kind in Wales. Sir Norman Lockyer has obtained measurements of most of these and plans showing the relations of the principal lines of their ground plan to the points of the compass, and so to the position occupied by the sun and by certain stars on given days of the year at the rising or setting of those heavenly bodies. It may well be asked what is Sir Norman’s object in doing this?

The explanation is as follows: The builders of Christian churches in Europe have, as a rule, set out the ground plan of the church shaped like a Latin cross, so that the arms of the cross run north and south—the head points to the east, or Orient, and the base to the west. In consequence of this custom the word “orientation” has come into use, to signify the direction purposely given to the main length of a temple or church. Now it appears that many, if not all, ancient temples (including the ancient stone circles and avenues of Britain) were purposely so “oriented” by their builders that a particular star, or the sun itself, should at a fixed day and hour in the year be seen during its movement across the heavens through an opening in the building especially designed for this purpose, so as to allow the light of the star to fall into the most sacred part of the temple, the “Naon,” or Holy of Holies. At the moment of its appearance special ceremonies were performed by the priests and worshippers in the temple. The temple was dedicated to and carefully “oriented to” that particular star. Thus, in ancient Greece, the Pleiades, Sirius (the dog star), Spica, and other stars were thus used; in Egypt, Capella, Canopus, and Alpha Centauri; in Britain, Arcturus, as well as those used by the Greeks.

These temples were really astronomical observatories, and were meant always to remain “oriented” to their special star, which must, if the earth were steady in its position, although spinning like a top, and also circling round the sun, duly appear each year at the expected day and minute in the special “window” or aperture designed so as to allow the star—then, and then only—to shine into the temple. But the astronomers have discovered that the earth is not steady! It “wobbles” very slowly and regularly as a top wobbles. The position of the axis of rotation—corresponding in position to the stem of a top—does not remain one and the same, but is pulled aside by the attraction of the sun and moon, and moves round as one may often see in the spinning of a top. The earth takes about 26,000 years for its poles to complete the cycle of its wobble. Moreover, in addition to this, there is the fact that the earth’s axis (stem of the top) is not nearly upright, but inclined at a considerable angle (23 deg.) to the horizontal or plane of its orbit round the sun, and that this inclination very slowly changes, in addition to the wobbling movement. The amount and rate of these changes in the inclination of the axis of the earth have been definitely ascertained by astronomers.

I mention the nature of these movements because they clearly enough must upset altogether the desired result of the orientation of temples. The last-mentioned slow increase of obliquity affects solar temples chiefly, and the more rapid wobbling affects the star temples—both to such a degree that temples oriented two or three thousand years ago are now quite out of line, and no longer “catch,” so to speak, their particular star or the sun on the appointed day. They no longer point truly, because the “pitch” of the earth has altered since they were set.

The next point is that astronomers are able to calculate with surprising accuracy from other observations how much exactly at this moment the “pointing,” or “alignment,” must be “out” as compared with a thousand, fifteen hundred, two, three, four, or more thousand years ago. Accordingly, if you know the star to which an ancient temple was set or aligned, the day of the solar year which was the festival or critical moment of the appearance of the star in the sacred aperture—and how much the temple is to-day out in its pointing, that is to say, the exact amount of swinging which would bring the temple back into its original relation to the star—you have a means of measuring the age of the temple; you have a measure of the time which has elapsed since it acquired this amount of departure from correct orientation. Astronomy tells you how much it must get out of line in every hundred years.

Mr. F. C. Penrose, F.R.S., investigated this matter in regard to several Greek temples; others besides Sir Norman Lockyer have written on the aberration and calculable age of Egyptian temples. It has, for instance, actually been found that the temple of Ptah was aligned to the sun in the year 5200 B.C. The alignment is no longer correct, and it appears that the Egyptians themselves discovered that some of their most ancient temples had lost correct alignment, and erected new and corrected buildings in connection with them, and re-dedicated them. Now Sir Norman is making a vigorous effort to procure all the possible measurements and indications concerning the prehistoric circles and avenues of Britain before it is too late. They are being more and more rapidly destroyed. Stonehenge has been carefully measured and its present alignment determined by various surveyors. Its age is discussed by Sir Norman Lockyer in an interesting book, but we may soon expect a further discussion of the whole subject of these prehistoric British monuments from his pen. In some cases, as in that of Stonehenge, the relation of the temple to the sun is obvious and confirmed by tradition and existing custom. But in many cases investigation is rendered very difficult by the absence of any immediate indication of what precisely is the heavenly body to which the temple was at its foundation oriented.

In the case of Stonehenge, the conclusion at which Sir Norman Lockyer arrives is that there was an earlier circle of small stones (still represented), but that the temple was rededicated, and the larger trilithons (each consisting of two uprights and a cross-piece) erected, and the main opening of the circle aligned to the midsummer rising sun about 1700 B.C., with a possible error of 200 years, more or less. This is arrived at by measurements showing the exact amount by which the alignment is “out” at the present day. This date is confirmed by the recent discovery of numerous stone hammers when one of the big stones was dug under and restored to the upright position from which it had slipped. The stone age is believed to have given place in Britain to the use of metal before 1700 B.C., and no metal tools were found at Stonehenge.

Stonehenge—the most wonderful, mysterious, and complete of the great astronomical temples of Western Europe—has come down to us from the absolute darkness of prehistoric ages. Its secrets are still buried in the ground around and under its huge monoliths. This prodigious relic of the past is actually the private possession of one happy man, Sir Edmund Antrobus. Only two years ago he earned the gratitude of all men by employing workmen and machinery, at considerable expense, to restore one of the great stones to its upright position. The extraordinary thing is that whatever money is needed for the purpose is not at once offered to enable him to examine and replace with scrupulous care every stone, big and small, every scrap of soil, within an area of many hundred yards, embracing Stonehenge and all around it. I understand that he is willing to sell this great possession to the nation. It surely ought to be acquired as national property, and reverently excavated and preserved, whilst every fragment of significance found in the excavations should be placed in a special museum at Amesbury or Salisbury, under unassailable guardianship. Year by year it has crumbled away. We owe the sincerest thanks to Sir Edmund Antrobus for having placed a light wire fence around the venerated relics, and for putting a guardian in charge so as to arrest, even at this latest moment, the final desecration and destruction of this splendid thing by heedless ruffians. The protection afforded is, nevertheless, insufficient. The delay in examining everything on the spot and in making all that remains absolutely secure is a national disgrace.