the mid-day sun was, within the limits of experiment, absolutely transparent to invisible radiant heat.

This then is the substance by which the invisible rays of the electric light may be almost perfectly detached from the visible ones. Concentrating by a small glass mirror, silvered in front, the rays emitted by the carbon points of the electric lamp, we obtain a convergent cone of light. Interposing in the path of this concentrated beam a cell containing the opaque solution of iodine, the light of the cone is utterly destroyed, while its invisible rays are scarcely, if at all, meddled with. These converge to a focus, at which, though nothing can be seen even in the darkest room, the following series of effects may be produced :

When a piece of black paper is placed in the focus, it is pierced by the invisible rays, as if a white-hot spear had been suddenly driven through it. The paper instantly blazes, without apparent contact with anything hot.

A piece of brown paper placed at the focus soon shows a red-hot, burning surface, extending over a considerable space of the paper, which finally bursts into flame.

The wood of a hat-box similarly placed, is rapidly burnt through. A pile of wood and shavings, on which the focus falls, is quickly ignited, and thus a fire may be set burning by the invisible rays.

A cigar or a pipe is immediately lighted when placed at the focus of invisible rays.

Disks of charred paper placed at the focus are raised to brilliant incandescence; charcoal is also ignited there.

A piece of charcoal, suspended in a glass receiver full of oxygen, is set on fire at the focus, burning with the splendour exhibited by this substance in an atmosphere of oxygen. The invisible rays, though they have passed through the receiver, still retain sufficient power to render the charcoal within it red-hot.

A mixture of oxygen and hydrogen is exploded in the dark focus, through the ignition of its envelope.

A strip of blackened zinc-foil placed at the focus is pierced and inflamed by the invisible rays. By gradually drawing the strip through the focus, it may be kept blazing with its characteristic purple light for a considerable time. This experiment is particularly beautiful.

Magnesium wire, presented suitably to the focus, burns with almost intolerable brilliancy.

The effects thus far described are, in part, due to chemical action. The substances placed at the dark focus are oxidizable ones, which, when heated sufficiently, are attacked by the atmospheric oxygen, ordinary combustion being the result. But the experiments may be freed from this impurity. A thin plate of charcoal, placed in vacuo, is raised to incandescence at the focus of invisible rays. Chemical action is here entirely excluded. A thin plate of silver or copper, with its surface slightly tarnished by the sulphide of the metal, so as to diminish its reflective power, is raised to incandescence either in vacuo or

in air. With sufficient battery-power and proper concentration, a plate of platinized platinum is rendered white-hot at the focus of invisible rays; and when the incandescent platinum is looked at through a prism, its light yields a complete and brilliant spectrum. In all these cases we have, in the first place, a perfectly invisible image of the coal points formed by the mirror; and no experiment hitherto made illustrates the identity of light and heat more forcibly than this one. When the plate of metal or of charcoal is placed at the focus, the invisible image raises it to incandescence, and thus prints itself visibly upon the plate. On drawing the coal points apart, or on causing them to approach each other, the thermograph of the points follows their motion. By cutting the plate of carbon along the boundary of the thermograph, we might obtain a second pair of coal points, of the same shape as the original ones, but turned upside down; and thus by the rays of the one pair of coal points, which are incompetent to excite vision, we may cause a second pair to emit all the rays of the spectrum.

The ultra-red radiation of the electric light is known to consist of ethereal undulations of greater length, and slower periods of recurrence, than those which excite vision. When, therefore, those long waves impinge upon a plate of platinum, and raise it to incandescence, their period of vibration is changed. The waves emitted by the platinum are shorter and of more rapid recurrence, than those falling upon it; the refrangibility being thereby raised, and the invisible rays rendered visible. Thirteen years ago, Professor Stokes proved that by the agency of sulphate of quinine, and various other substances, the ultraviolet rays of the spectrum could be rendered visible. These invisible rays of high refrangibility, impinging upon a proper medium, cause the molecules of that medium to oscillate in slower periods than those of the incident waves. In this case, therefore, the invisible rays are rendered visible by the lowering of their refrangibility; while in the experiments of the speaker, the ultra-red rays are rendered visible by the raising of their refrangibility. To the phenomena brought to light by Professor Stokes, the term fluorescence has been applied by their discoverer, and to the phenomena brought forward this evening at the Royal Institution, it was proposed to apply the term calorescence.

It was the discovery, more than three years ago, of a substance opaque to light, and almost perfectly transparent to radiant heat-a substance which cut the visible spectrum of the electric light sharply off at the extremity of the red, and left the ultra-red radiation almost untouched, that led the speaker to the foregoing results. They lay directly in the path of his investigation; and it was only the diversion of his attention to subjects of more immediate interest that prevented him from reaching, much earlier, the point which he has now attained. On this, however, he can found no claim; and the idea of rendering ultra-red rays visible, though arrived at independently, does not by right belong to him. The right to a scientific idea or discovery is secured by the act of publication; and, in virtue of such an act, priority of conception as regards the conversion of

heat-rays into light-rays belongs indisputably to Dr. Akin. At the meeting of the British Association, assembled at Newcastle in 1863, he proposed three experiments by which he intended to solve this question. He afterwards became associated with an accomplished man of science, Mr. Griffith of Oxford, and jointly with him pursued the inquiry. Two out of the three experiments proposed at Newcastle by Dr. Akin are impracticable. In the third, Dr. Akin proposed to converge the rays of the sun by a concave mirror, to cut off the light by proper absorbents,' and to bring platinum foil into the focus of invisible rays. It is quite possible, that, had he possessed the instrumental means at the speaker's disposal, or had he been sustained as the speaker had been both by the Royal Society and the Royal Institution, Dr. Akin might have been the first to effect the conversion of the dark heat-rays into luminous ones. For many years the idea of forming an intense focus of invisible rays had been perfectly clear before the speaker's mind; and in 1862 he published experiments uponthe subject. The effects observed by him in 1862 at the focus of invisible rays were such as no previous experimenter had witnessed, and no experimenter could have observed them without being driven to the results which formed the subject of the evening's discourse. Still publication is the sole test of scientific priority; and it cannot be denied that Dr. Akin was the first to propose definitely to change the refrangibility of the ultra-red rays of the spectrum, by causing them to raise platinum foil to incandescence.

WEEKLY EVENING MEETING,

Friday, January 27, 1865.

[J. T.]

SIR HENRY HOLLAND, Bart. M.D. D.C.L. F.R.S. Vice-President, in the Chair.

Major-General Sir HENRY C. RAWLINSON, K.C.B. D.C.L. F.R.S.

On the results of Cuneiform Discovery up to the present time.

SIR HENRY commenced by observing that the time had gone by when it was necessary to defend the system of Cuneiform Decipherment from the attacks of the incredulous. The school of sceptics, led on by the late Sir G. Lewis and his friends, had passed away. France and Germany, which were at first slow to believe, had now fairly given in their adhesion, and admitted Assyrian studies into the recognized category of linguistic science. The Institute of France, indeed, had last year conferred its biennial prize of 20,000 francs on M. Oppêrt, for his labours on the Assyrian Inscriptions, thereby testifying, in the face of Europe, to the genuineness and value of his researches.

In England, the Cuneiform decipherers were no longer looked upon as visionaries or impostors. The tone of the public press had become, at any rate, respectful, and anxiety was beginning to be shown for authentic information on the subject.

Assuming, then, that there was no occasion to recapitulate the arguments, which he had advanced in a former discourse in that room, in support of the general principles of his method of Decipherment. Sir Henry went on to say, that great caution was still required to be exercised in discriminating between guess-work and demonstration, and in accepting the results put forward by different enquirers. M, Oppêrt, for instance, had contributed an article on the "Tower of Babel," to Dr. Smith's "Dictionary of the Bible," asserting that the name of Borsippa, which attached to the site where the tower was traditionally believed to have stood, was etymologically connected with "the confusion of tongues," and that there was also a distinct allusion to the same event in the inscription on the cylinders found in the ruins of the Borsippa Temple; and this remarkable notice, transferred to the pages of a recent number of the "Quarterly Review," had naturally attracted much attention amongst Biblical students, authenticating, as it seemed to do, one of the earliest and most important portions of the Scripture narrative. There was in reality, however, no foundation whatever for M. Oppêrt's statement. He had misinterpreted certain expressions, and at once jumped to the conclusion that he had really found a trace of Noachidan history. As far as Sir Henry's own researches extended, not a single allusion had been discovered in the inscriptions, either of Assyria or Babylonia, to the leading events of the Mosaic record. It seemed probable, indeed, that the earliest native Babylonian notices did not reach as high as the period of Chedorlaoiner and his confederate kings; for at that time Elam was evidently in the ascendant, and the provinces to the westward were mere tributaries, whereas when Cuneiform history first dawns on us, we find the Turanian tribes of the Accad and their allies, represented in the Bible by the goim, or "nations," of whom Tidal (properly, Tur-gal, "the great chief") was king, exercising independent sway in Southern Chaldea.

Sir Henry then, referring to diagrams suspended on the wall, proceeded to explain his own views with regard to the early comparative chronology of Assyria and Babylonia, as revealed to us from the Cuneiform Inscriptions. He showed, in the first place, that there was an authentic date reaching as high as the 19th century B.C. Whether the Ismi-dagon, who built a temple in Assyria at this period, was really the king of the same name, whose bricks had been found in the ruins of Ur of the Chaldees, did not much signify. It was sufficient to know that the Assyrians really had materials for history, ascending to a period of such remote antiquity. He believed himself, that the Assyrian "Empire," succeeding the rule of the high-priests, commenced in the 18th century B.C. synchronously, perhaps, with the establishment of a Turanian dynasty in Babylon. To the latter,

on the authority of Berosus, he assigned a duration of 450 years, supposing that in about B.C. 1300, Tilgamus of Assyria had driven out these Turanians, and established a junior branch of the Royal family of Nineveh on the throne of Babylon, which family had remained in power until shortly before the era of Nabonassar in B.C. 747. The great line of Assyrian royalty had, probably, remained unbroken from the first establishment of the Empire in the 18th century B.C. to the death of Shalmaneser IV. at the siege of Samaria, in B.C. 721, and the remaining kings, from Sargon downwards, who, if belonging to the royal family, did not, at any rate, succeed in the direct line of hereditary descent, formed what was generally called the Lower dynasty.

A most important aid for determining the dates of the later Assyrian history, and for rectifying, by means of these dates, the general scheme of Scripture chronology, had been recently obtained, through the discovery, among the Nineveh tablets in the British Museum, of a table of Archons, or Eponymes, extending over a period of 270 years. It had been the custom at Nineveh, as at Athens, to name the year after a particular officer, and a series of these names, therefore, formed an official chronological table. Fragments of four such tables had been found, the reigns of the kings, moreover, being marked by a line drawn across the column of names, and students were thus able within the limits of the series, or from about B.C. 910 to 640, to determine the relative date of all the leading events in the history of Western Asia. The effect of this was to lower the date of Jehu and his contemporaries by about forty years.

Sir Henry then went on to show from a diagram, explaining the canon, the various synchronisms of Assyrian and Jewish history, down to the time of the great Sardanapalus, who was, he stated, the son of the Biblical Esar-Haddon. The reign of Sardanapalus afforded the only point of contact between the history of Nineveh and the history of Greece, the Assyrian empire expiring just as the Grecian power arose. The dodecarchy of Egypt, described by Herodotus, was shown to have been instituted by Sardanapalus, and the same king received an offering of Cimmerian slaves from Gyges, the king of Lydia, who played so prominent a part both in Grecian history and fable.

In a later part of his discourse, Sir Henry commented on the contents of many of the tablets which he had been recently examining,* and of which the following was a list :

1. Syllabaries, or lists, explaining the phonetic powers and meanings of all the Assyrian simple and compound characters and monograms.

These "terra-cotta" tablets, which form the most valuable portion of the Assyrian collection in the British Museum, were exhumed from the ruins of the palace of Sardanapalus at Nineveh, being in fact the debris of the Royal Library. There are probably as many as 100,000 fragments of such tablets now ranged on the shelves of our national museum, but a very small portion are legible, and a still smaller portion sufficiently perfect to give the sense of the document to which they belong.