THE

HE Museums d'Histoire naturelle, in the beautiful surroundings of the Jardin des Plantes in Paris, founded in 1793, form an institution of acknowledged eminence; whilst the lectures delivered there are by the most renowned professors, and on most, if not all, branches of the natural sciences. It was Cardinal Richelieu, as we know, who founded the Jardin des Plantes somewhere about 1626, not long before the establishment of the French Academy by the same great Minister of State.

The physical laboratory in particular of these museums has been the seat of many discoveries and the centre from which has radiated some of the best thought, as well as some of the best work, that has animated the academy and through it the scientific world for three-quarters of a century. It is not often the case with science, nor, indeed, with other branches of learning, that in a single family there should be found for three generations a series of distinguished men of the highest order of intellect who have devoted their lives and best energies to its pursuit and attained to universal fame. More seldom is it, then, that when the lineage is thus preserved unbroken, the members thereof should all be devoted to the one and to the self-same calling. For three generations the Becquerels have occupied in succession the same chair at the same institution, namely, the Museum d'Histoire naturelle in Paris. The number of papers which have been read before the Academie des Sciences by the Becquerels extends to seven or eight hundred.

Henri Becquerel, whose portrait in his laboratory at the Museum d'Histoire naturelle is here reproduced, is, we venture to think, perhaps the most distinguished of his race. His father, Alexander Edmond, is known as the inventor of the phosphoroscope and the author of "La Lumière," a work of great value in its day, whilst his grandfather, Antoine César, was likewise famous for a long series of researches, chiefly on chemical dynamics and electrocapillary phenomena. His electromagnetic balance is of historic

It was not so with other scientific centres of this series; there there were many discontinuities, here the continuity is one.

The technical process of gilding due to de la Rive was based upon Becquerel's observation in 1834 of the deposition of metals on the negative electrode when the poles of a pile are immersed in solutions of various metallic salts; that the two solutions needed could be kept apart by the use of animal membranes without preventing the passage of the current, and that with very feeble currents the deposition of metal is even

and uniform on the surface of the electrode. Although rivalled by many others in the application of these principles, many were the facts and many the methods which he announced with rapid succession in laying the foundations of the art of electro-plating.

It was to the study of electrocapillary phenomena, which he was the first to observe in 1867, that his later years were devoted. The discovery was a curious one, the result, if we mistake not, of the deposition of

metallic copper on a crack in a test-tube containing a solution of cupric sulphate, and immersed in another solution of sodic sulphide. The investigation of this phenomenon was full of interest, and not the least was the suggestion that the deposition of metals in veins in rocks is due to the same cause as that which he observed in the broken test-tube.

A member of the French Academy from 1829, eight years before being called to the chair which he filled to the end of his life, he was also a corresponding member of the Royal Society, and received from it its greatest honour, the Copley medal, and from the Emperor Napoleon III. the Cross of Commander of the Legion of Honour. Thus with him there closed a chapter, a long, an interesting, and an eventful chapter, in the history of the Museums d'Histoire naturelle.

gates which gradually disintegrate, as radio-active molecules have been found to do, the change of absorption which accompanies fluorescence being due to the formation of these molecular groups.

The absorption spectrum of crystals exhibits many anomalies, from which Becquerel has extracted a most important principle. If a crystal is composed of two isomorphous substances the molecular elasticity of which varies in different directions, so that the absorp tion varies too, the absorption spectrum will likewise vary in different directions, so that it is thus possible to detect the presence of different substances, since in two isomorphous substances the directions of molecular elasticity do not correspond, and therefore the directions of absorption would likewise differ. Each chemical substance, therefore, affects the direction of propagation and of absorption.

career.

At the death of his father, in 1878, he succeeded to the chair of physics at the museum, and this important position he continued to hold until his death in 1892. Brought up as he was in a scientific atmosphere, he evidently inherited from his father his "acute power of observation," and that "infinite capacity of taking pains which seems to be the essential characteristic of the Newtons, the Faradays, and the Darwins, and, in short, of all the great leaders of science."

Since 1892 Henri Becquerel has been professor at the Museum d'Histoire naturelle, and has continued those studies which his ancestors in days gone by pursued with ardour and with success, not the less marked, although perhaps, on the whole, notwithstanding their brilliant achievements, less fruitful in revealing that knowledge which was to come; for by his memoirs on the radio-activity of matter Henri Becquerel has given to the world of science the results of a very remarkable series of researches.

There are four methods of studying the infra-red parts of the spectrum: the thermopile, as employed by Tyndall and others, the radiomicrometer of Boys, the bolometer as used by Langley, and the phosphorescent screen of Becquerel. After exposure to the violet rays, and if the screen is subjected to the action of the infra-red, the phosphorescence becomes so intense that the energy accumulated is radiated so rapidly that the parts thus acted upon become quite dark relatively to the other parts of the screen. Thus a map of the infra-red can be produced and studied at leisure so long as the phosphorescence of the screen lasts, or, indeed, photographs of the screen thus affected may be taken. The effect is due most probably to heat, and is therefore a case of thermoluminescence. Under the influence of heat the collisions between molecules become more frequent and more violent, and the energy absorbed from the more refrangible rays, and stored up in the substance, by some means at present not very clearly understood, is once more yielded up to the æther and radiated away. The energy is stored up in unstable molecular aggre

this elegant method of analysis.

But the most striking work that has issued from Becquerel's laboratory relates to the radio-activity of matter. Of this great discovery, separating as it does the ideas of this century from those of the last, so much has been written, upon their far-reaching importance, so many ideas have been discussed in these columns, that to discourse upon them here would be but vain repetition of all that has been said before; yet, paradoxical though it may seem, it is unquestionably the work of all works that most definitely separates, and at the same time most closely unites, the two sciences of physics and chemistry, whilst it brings into prominence what may appropriately be called a new sciencethat of radio-activity-a science which neither physics nor chemistry can claim within its old province, and yet neither can disclaim, nor would it very readily do so if it could.

What is the influence which these laboratories have exerted and exert? We may ask, what is the influence of the Royal Institution? Is it not to be measured by the work which has been done there and by the ideas which have been scattered from those great fountains of thought-if they can be measured? How many youthful imaginations, how many enthusiastic aspirations have been aroused within those venerable halls, of the Becquerels as of the Davys, the Faradays, and the Tyndalls? Parisian lecturers are savants, philosophers, and orators. For although the Teuton regards the gift of eloquence (we hope it is his own) as the gift to be designated as gab, the southerner or the Celt thinks it indispensable in the expression of a clear mind and of a great soul, at once saturated with thoughts and the grandeur of its subject; and in France this counts for more than it usually does among us.

66

These lectures are a source of inspiration to the multitude as well as to the grave, and their importance cannot be overrated.

Having said thus much of the laboratories of the Museum d'Histoire naturelle, we may perhaps be permitted to add a word as to the central figure in this centre of scientific thought, of M. Henri Becquerel; from none need we expect greater freedom, greater ease, or kindlier consideration. The brief summary

1 British Association and Electrician, 1900-02; and Phil. Mag., 1901 Phil. Trans., 1897

LONDON

"NATURE" says:

"The new illustrated catalogue of physical apparatus just issued by Messrs. F. E. Becker and Co. (Messrs. W. and J. George, Ltd.) is likely to prove indispensable in the physical laboratories of all our schools and colleges. It runs to 628 large pages, and is strongly bound in cloth. Full particulars are provided, not only respecting the apparatus required in elementary and advanced physical teaching, but also concerning that necessary to the physicist in his research work. All branches of physics are included, and the instruments throughout are explained by excellent illustrations and concise descriptions, and, what is of prime importance, the figure and its appropriate text are close together."

"CHEMICAL NEWS" says:

as

"Messrs. F. E. Becker and Co. (W. and J. George, Ltd., successors) have just issued a new Illustrated and Descriptive Catalogue of Physical Apparatus, This is &c., manufactured by them. the largest and best English catalogue of its kind printed, and comprises some 680 pages and over 4,000 illustrations; herein will be found all the newest up to date apparatus with all the latest at improvements manufactured their works, while all obsolete apparatus has been omitted. The whole catalogue is arranged in a very clear manner under a number of principal headings, such as Magnetism, Heat, Sound, Light, Mechanics, Electricity, Pneumatics, Meteorology, X-ray Apparatus, &c., and a good index is provided; in fact, everything possible has been done to make this as perfect a guide as possible to users of apparatus in the subjects touched upon.'

"KNOWLEDGE" says:

"Messrs. F. E. Becker and Co. (W. and

J. George, Ltd., Successors) have sent us a copy of their new list of apparatus in the various departments of Physics, including Sound, Light, Heat, Magnetism, Electricity, Mechanics, &c. This exhaustive catalogue consists of over 600 pages and some 4000 illustrations. One of its noteworthy features is that the requirements of science teaching in this country and its colonies are always kept in view, and the articles listed cover the latest developments in their subjects. The method adopted in the list itself, together with the completeness of the index, is such as to make reference to it simple and expeditious."

"SCHOOL WORLD

says:

"The science-master in every grade of school should possess a copy of the new catalogue of Messrs. George, for he will find here particulars as to the available apparatus in sound, light, heat, magnetism, electricity, mechanics, and other branches of physics, with information as to price and other necessary details. There is a profusion of welldrawn illustrations, which, together with the clearly expressed descriptions, will serve to explain to any buyer exactly what he is purchasing. This excellent catalogue will form a valuable addition to the reference library of any physical laboratory."

LONDON

SECOND-HAND TELESCOPES.

4 in. ALVAN CLARK, with Slow Motions, £50; 3 in. STEWARD, with Slow Motions, cost £60, £25; 9 in. CALVER, Equatorial with Clock, Universal Mount, Mirror by WITH, £45.

List, including many others, on application. SECOND-HAND MICROSCOPES. WATSON'S Edinburgh H., £16; SWIFT's Bacteriological, £18 10s.:

Best Make and Finish.

SET SQUARES,

T SQUARES, DRAWING BOARDS.

List, including many others, on application.

A. CLARKSON & CO.,

28 BARTLETT'S BUILDINGS, HOLBORN CIRCUS, LONDON, E.C.

Obtained through any Optician.

ROBERT NICHOLL, 153 HIGH HOLBORN, LONDON.

THE IRISH NATURALIST.

A Monthly Magazine of Irish Zoology, Botany, and
Geology. Price 6d.

Edited by GEO. H. CARPENTER, B.Sc., and R. LLOYD
PRAEGER, B.A.

Annual Subscription, 5s. Post Free to any Address.
Dublin: EASON & SON, LTD., 40 Lower Sackville Street
(to which Address Subscriptions should be sent).

London: SIMPKIN, MARSHALL, HAMILTON, KENT, & CO., Ltd.

THE ENTOMOLOGISTS' MONTHLY

MAGAZINE.

Price Sixpence, Monthly.

Edited by G. C. CHAMPION, F.Z.S., J. W. DOUGLAS, W. W. FOWLER, M.A., F.L.S., R. MCLACHLAN. F.R.S., E. SAUNDERS, F.L.S., and LORD WALSINGHAM, M.A., LL.D., F.R.S.

This Magazine, commenced in 1864, contains standard articles and notes on all subjects connected with Entomology, and especially on the Insects of the British Isles.

Subscription-Six Shillings per Annum, post free.

London: GURNEY & JACKSON (Mr. Van Voorst's Successors), I Paternoster Row.