has already written its own history on the present, and the interpretation of the record is a question not of possibility, but of time and perseverance. "But for the present, we must content ourselves with much humbler results. It is much if the clouds of ignorance are in places clearing away; if from the summit which we occupy we can catch occasional glimpses of the distant past far away beneath our feet. "So far as these Lake-habitations are concerned, and so far as one short hour would permit, I have endeavoured to give you a faithful account of the discoveries already made, and in doing so have confined myself almost entirely to a simple statement of facts; fearing, lest perhaps imagination, tempted by opportunity, might lead us away from truth. For imagination is a bad master, though a good servant; and yet it is almost as necessary to progress in science and the arts as heat is to life. "From the stamped bricks of Assyria to the modern printing-press seems but a step; and yet mankind hovered on the brink of discovery for more than 3000 years. So again the piles in the Swiss lakes had long been known, objects of antiquity had even been found among them; yet these were in themselves but barren observations, and have might so remained until now, if the genius of Dr. Keller had not supplied the spark which kindled the dead facts into a living science. "And yet science is considered by many, perhaps by most of us, as hard, dry, and unpoetical. If the absolute necessity of teaching in our schools some few of the discoveries made in the last 1800 years, is day by day more generally recognized, still it is rather regarded as an evil, than welcomed as a blessing, from the fear lest, in developing the memory, we might tend perhaps to cramp the imagination. Yet science is not only truer, but more sublime than mythology; grander than the disreputable deities of the Greeks, or the old fairy tales of Europe. "Poets have invented no monsters more wonderful than those which geology has revealed to us. The laws of nature are more powerful and more subtle than any of the genii in the Arabian Nights'; and the philosopher who can place himself in harmony with nature, and avail himself of the opportunities by which he is surrounded, need envy neither Merlin his magic, nor Aladdin his lamp. "Can anything be more magnificent than the last triumph of chemistry, when, not content with the conquest of this world, she soars into the heavens, and by means of his own light, analyzes the sun himself? Or turning once more finally, and but for a moment, to our immediate subject, surely his imagination must be dead indeed who feels no emotion at the spectacle of an ancient and long-forgotten people, after slumbering for centuries in the grave of oblivion, rising thus, as it were, to take once more that place which properly belongs to it in the history of the human race." [I trust that I may be permitted here to acknowledge the great courtesy which I received from Dr. Keller, Prof. Desor, Col. Schwab, MM. Forel, Ullmann, and Rochat, and indeed from all the Swiss archæologists. Col. Suter and M. Gilliéron also most kindly gave me an opportunity of examining for myself the Lake-dwellings at Wauwyl and the Pont de Thiele, which they have respectively so well studied. But to M. Morlot my thanks are chiefly due, for having devoted to me a month of his valuable time, and for other acts of kindness too numerous to be specially mentioned.] [J. L.] GENERAL MONTHLY MEETING, Monday, March 2, 1863. WILLIAM POLE, Esq. M.A. F.R.S. Treasurer and Vice-President, in the Chair. Edward Atkinson, Esq. The Rev. Henry Blunt, Henry Lainson, Esq. William McKeand, Esq. John Rutherford Russell, M.D. were elected Members of the Royal Institution. The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same: viz.— FROM Secretary of State for India-Rig-Veda Sanhitá: the Sacred Hymns of the Brahmans. Edited by Max Müller. Vol. IV. 4to. 1862. Geological Survey (through Sir R. I. Murchison)-Mineral Statistics. 1860-61. Memoirs. Six Parts. 1859-62. 8vo. French Government (through M.G. Rouland, Minister of Public Instruction)—Documents Inédits sur l'Histoire de France : Le Mistère du Siége d'Orléans. Ed. F. Guessard et E. D. Certain. 4to. 1862. Mémoires de N. J. Foucault. Ed. F. Baudry. 4to. 1862. Négociations de la France Tome II. 4to. 1861. (1661-72.) 4to. avec la Toscane. Ed. A. Desjardins. Journal d'Olivier Lefevre D'Ormesson. Ed. M. Cheruel. 1861. Tome II. Lettres, &c. du Cardinal de Richelieu. Ed. M. Avenel. Tome IV. 4to. 1861. American Philosophical Society-Proceedings, No. 68. 8vo. 1862. 8vo. Best, Hon. and Rev. S. M.R.I.-Papers read on the Ninth Anniversary of the Southern Counties Adult Education Society. (K 89) 8vo. 1862. British Meteorological Society-Report for 1861. 8vo. Proceedings, 1862. Nos. 1, 2, 3, 4. 8vo. Chemical Society-Journal, 1863. No. 1. 8vo. Editors-Artizan for February, 1863. 4to. Engineer for February, 1863. fol. Journal of Gas-Lighting for February, 1863. 4to. Practical Mechanics' Journal for February, 1863. 4to. 8vo. 1863. Horticultural Society, Royal-Proceedings, 1863. No. 2. 8vo. 1863. Newton, Messrs.-London Journal (New Series) for February, 1863. 8vo. Petermann, A. Esq. (the Editor)-Mittheilungen aus dem Gesammtgebiete der Geographie. No. 1. 4to. 1863. Photographic Society-Journal, No. 130. 8vo. 1863. Royal Society of London-Proceedings, No. 53. 8vo. 1862. Silliman, Professor-American Journal of Science, &c. for January 1863. 8vo. Tyndall, Professor J. F.R.S. M.R.I. (the Author)---Heat considered as a mode of Motion: being a Course of Twelve Lectures, delivered at the Royal Institution in 1862. 16to. 1863. United Service Institution, Royal-Journal, No. 24. 8vo. 1862. Walford, W. S. Esq. M.R.I.—La Manere de Tenere Parlement (in French.) Ed. by T. D. Hardy. [Bound with "Modus tenendi Parliamentum."] 8vo. 1862. WEEKLY EVENING MEETING, Friday, March 6, 1863. SIR HENRY HOLLAND, Bart. M.D. D.C.L. F.R.S. Vice-President, in the Chair. WILLIAM ALLEN MILLER, M.D. Treasurer R.S. On the Photographic Transparency of Bodies, and on the Photographic Spectra of the Elementary Bodies. AFTER a few preliminary remarks upon the triple nature of the force, calorific, luminous, and chemical, associated together in the radiation which emanates from luminous sources, the speaker stated his intention of limiting himself in great measure to some recent investigations upon the chemical rays.* It is well known that bodies which are transparent to light are not equally so to radiant heat. Glass, for example, which to the eye is perfectly transparent and limpid, arrests a large portion of the rays of heat emitted by bodies which are not sufficiently hot to become luminous. Pure rock-salt, on the other hand, transmits rays of both light and heat from all sources freely. In like manner, in the case of rays which produce chemical action, corresponding effects have been observed; glass absorbing many of the chemical rays, whilst quartz transmits such rays freely. The chemical rays emitted by luminous objects vary greatly both in quantity and in quality, some sources of light emitting rays of much higher refrangibility than others. Thus, the flame of ordinary coalgas burned in admixture with air, so as to produce the blue light of a smokeless gas flame, gives out scarcely any rays capable of affecting an ordinary photographic plate; whilst the same amount of gas, burned The expressions here employed are simply used as descriptive of the effects ordinarily produced by the different portions of the spectrum, not as necessarily implying that the rays which produce the effects of heat, light, and chemical action respectively are essentially different, except in the number and frequency of the vibrations by which they are produced, the most refrangible rays being produced by the shortest and most frequent vibrations. in the ordinary manner for illumination, emits a very decided though limited amount of rays capable of producing chemical action. The rays emanating from the intensely hot jet of the oxyhydrogen flame, are nearly without action upon a sensitive surface of collodion; whilst if thrown upon a ball of lime, the light then emitted contains as large a proportion of chemical rays as the solar light, and of very nearly the same refrangibility. But the most remarkable source of the chemical rays is afforded by the light of the electric spark or of the voltaic arc, the chemical spectrum of which is three or four times as long as the chemical spectrum obtainable from the sun itself. 1. Photographic Transparency of various Media.-Amongst the methods of testing the extent of chemical action of any given radiant source, the most convenient is that which is dependent upon the extent of photographic effect exerted upon a surface of collodion coated with iodide of silver, on which the spectrum is allowed to fall. In no case does it appear that any non-luminous source can emit chemical rays of sufficient intensity to traverse ordinary refracting media; and amongst the rays given off by various luminous objects, it is found that the chemical effects upon the collodion plate are not perceptible in those portions upon which the first three-fourths of the visible spectrum has fallen, but they commence powerfully in the last fourth; and in the case of the electric spark are prolonged to an extent equal to between four and five times the length of the visible portion. A diagram exhibiting the relative lengths of the visible solar spectrum, and the photographic spectrum obtained from the electric spark between silver points, showed this fact in a striking manner. It was known to those who have studied the spectrum, that many lourless substances besides glass exert an absorptive action upon some of these chemical rays; but the subject had not hitherto received that careful experimental examination which its importance seems to warrant. Exact knowledge upon these points became requisite in the course of an investigation upon the photographic spectra of the metals in which the speaker was engaged. In the prosecution of these inquiries it was a desideratum to procure some substance which should possess a higher dispersive power than quartz, and which, whilst avoiding the double refraction of quartz, should yet allow the free passage of the chemical rays. The speaker was hence led to try a variety of substances which, owing to their transparency to light, might reasonably be hoped to possess chemical transparency also. The inquiry soon extended itself beyond the limits originally proposed, and ultimately embraced a large number of bodies in the solid, liquid, and gaseous conditions. Before, however, proceeding to detail the results obtained, the speaker alluded to the discovery of Professor Stokes, that many bodies exist which, when placed in the invisible extra-violet, or more refrangible portion of the spectrum, exhibit the remarkable power of absorbing |