cellular animals to the Metazoa, and his embryological theory of the "phagocytella." The reaction of the mesodermic phagocytes of sponges to foreign matters introduced into the substance of these animals is described; and, subsequently, similar phenomena in Colentera, Echinoderma, and Worms are cited, and illustrated by original drawings. It is shown that in these Invertebrates the phagocytes attack and invest, either singly or in fused masses, not only inorganic particles, but large parasites, and also intrusive parasitic Bacteria. Thence he passes to organisms-the Mollusca, Arthropoda, and Tunicata--which have a well-developed blood-system. He shows that here, too, there are no special "vascular" phenomena excited by conditions which in higher Vertebrates produce "inflammation," but solely a phagocyte reaction" or resistance. Numerous cases of infectious bacterial and fungal diseases in Arthropoda are described, and the action of the phagocytes in combating the intrusive parasites by ingulfing and digesting them is demonstrated. Even when we come to the Vertebrates, it is shown that, in regions of the median fin of the tadpole of the Axolotl, an inflammation can be excited which is purely phagocytic, and in which the bloodvessels and their contents take no part.

The peculiarity, however, of inflammatory processes in adult and higher Vertebrata is, that the blood-vessels come into play. The amoeboid corpuscles floating in the blood by active movement (of a chemiotactic nature), push their way through the walls of the capillaries (diapedesis) in the region which is infected or injured, and join their forces to those of the tissue phagocytes in investing and destroying the injurious particles.

A detailed study of the leucocytes of the blood and lymph of Vertebrates follows, which are distinguished as (1) lymphocytes, (2) uninuclear, (3) eosinophil, and (4) neutrophil or multinuclear leucocytes. Metschnikoff shows that the two varieties of leucocytes which play the chief part in inflammation-viz. the uninuclear and the neutrophil-are endowed with a marked chemiotactic and physiotactic sensibility, are capable of amoeboid movements, and apt to ingulf and to digest various foreign bodies, notably many kinds of living Bacteria. In the Amphibia he shows that the multinuclear leucocytes can transform themselves into the uninuclear form, and become fixed cells of the connective tissue. In Vertebrates generally, uninuclear leucocytes can be transformed into epithelioid and giant cells. What is true of leucocytes is also true of other migratory cells.

The ninth, tenth, and eleventh lectures deal with such topics as the endothelium of vessels, the dilatation of vessels, chronic inflammations-tubercle being taken as a type-serous inflammation, bactericidal power of serous humours and exudations; and the antitoxic property of the serum. A most important and interesting study of

I cannot let pass this opportunity of pointing out an evolutional parallel in the history of phagocytes which tends to harmonize to some extent the views of those who insist on the bactericidal and the anti-toxic properties of serum, with Metschnikoff's view that the phagocytes are of prime importance. In the recent debate at the Pathological Society of London, it was pointed out by several speakers that even if it be admitted that the serum and exudations have, in relation to certain special cases, these propertiesor rather contain substances having these properties-those substances must be derived from the living cells of the organism, and probably from leucocytes. The parallel to which I refer is that of intra-cellular and cavitary digestion. The alimentary canal of some lower animals is lined by phago.

the phenomena of resistance to the tubercle bacillus on the part of the giant-cells of the Algerian Rodent Meriones Shawi is given in some detail.

The last lecture treats of some previous theories of inflammation, summarizes the facts which serve to establish what Metschnikoff calls the biological theory of inflammation, and repels some attacks recently made on it. The theory is formulated in these words: "Inflammation must be looked upon in its entirety as a phagocytic reaction of the organism against irritative agents— a reaction which sometimes is carried out by wandering phagocytes only, sometimes with the assistance of the vascular phagocytes or with that of the nervous system.” The last words refer to the intervention of the vaso-motor nervous centres.

Medicine, says our author in order to gain her assigned objects must make use of knowledge drawn from all less complicated branches of science; and amongst others from that biology which studies organisms in their living state and their natural evolution.

The services rendered will be reciprocal. General biology, he points out, can gain great advantage by embracing in the sphere of its studies the morbid phenomena now relegated to the pathologist. Too often biology finds difficulties in the study of the processes of evolution because the phenomena are presented to the observer in an already accomplished form. To observe with clearness the play of the general law of natural selection, we must study the less stable phenomena, the less perfected organizations—in a word, the phenomena in which natural selection can be observed every day. Now it is precisely the phenomena of disease and the reactions connected with it-the struggle between the organism and its aggressors which offer the best opportunity for a close study of the operation of natural selection.

It has been impossible to do justice to this remarkable book in a short review. It has the special quality of carrying conviction to the reader's mind by the fact that every assertion is supported by a number of wellchosen observations or experiments which are described with a lucidity and precision characteristic of a man thoroughly familiar with the minutest details of the things of which he speaks. It is to be hoped that it may have, amongst other consequences, that of silencing certain medical "educationists," who deny that zoology is a necessary or useful accompaniment of the chemical and physical study of living things. Its pages contain convincing proof that medicine has gained more real knowledge and practical help from modern zoology than from the elaborate experimentation on higher Vertebrates which is directed by narrow-minded ignorance of the simpler expressions of animal organization.

E. RAY LANKESTER.

cytes, which individually ingulf solid particles of food, and digest them by means of ferments, acids, &c., formed within the phagocytes. A later stage of evolution of the digestive system consists in the discharge by these cells of the food-dissolving substances elaborated by them into the common liquid occupying the cavity which they surround. The food dissolving substances are no longer found exclusively in the cells, but in the liquid which bathes them. Yet no one ascribes a special power to the gastric juice, or hesitates to trace its qualities to the transformed intra-cellularly-digesting cells, S with bactericidal and anti-toxic juices: they must be traced (when their existence is proved) to the modification of the modus operandi of intracellularly-digesting phagocytes.

THE

HE first of these two books deals with a part of the period during which the late Dr. Junker carried on his second series of explorations in Central Africa. On his return to St. Petersburg in September 1878, after his first journey to the Egyptian Sudan, he had no intention of paying another visit to that region. Nevertheless, within a year he was hard at work preparing for a similar expedition, and on October 10, 1879, he found himself on board the steamer which took him to Alexandria. With as little loss of time as possible he made for Khartum, whence he started by the Ismailia, on January 31, 1880, for Meshra Er-Req, on the Bahr el-Ghazal. This part of the journey was made extremely tedious by the "sudd," or grass-barriers, through which the steamer had to force its way. The vegetation of which "sudd" is composed grows luxuriantly in back-waters; and great masses of it are brought by winds or by flood-waters into the river. These masses may either drift harmlessly with the currents, or coalesce into formidable barriers. Sometimes they become so compact that a steamer cannot penetrate them, and they must be broken up by special apparatus. This is especially the case in the Bahr el-Jebel. In the Bahr el-Ghazal the barriers are troublesome enough, but are not of quite so tough a texture.

At Meshra Er-Req Dr. Junker met Gessi Pasha, who was at that time Governor of all the Equatorial Provinces. The two men had a warm regard for one another; and after a little delay, due to Gessi's numerous engagements, they made an excursion together to Dem Soliman, the most important of the Arab settlements visited by Dr. Junker in the negro lands. Here they parted, never to see one another again, for Gessi died about two years afterwards at Suez. From Dem Soliman Dr. Junker travelled in a south-easterly direction to the territory of Ndoruma, a native chief, who, although rather fickle, was of considerable service to him. In this territory, on the banks of the Werra, Dr. Junker established a station called Lacrima, where he remained about two months. He then proceeded southward, crossing the Welle, and residing some time with Prince Mambanga, from whose territory he went eastward to Tangasi. Before the end of 1880 he was back at Lacrima, which he had left in charge of his companion, Bohndorff. In the course of 1881 Dr. Junker travelled among several different tribes, arriving about the end of the year at the domain of Prince Bakangai from Hawash station. At this point the narrative stops, to be continued, no doubt, in another volume, although on this point nothing is said either by the translator or by the publishers.

So many changes have taken place since 1881 in the regions visited by Dr. Junker that his account of the mutual relations of the native tribes is now, of course, out of date; but that does not in any way diminish the

value of his descriptions of their permanent characteristics. He had a remarkable power of winning the confidence and respect of the people, and thus had many opportunities of forming a trustworthy estimate of their intellectual and moral faculties. Upon the whole, the impression they produced upon him was not unfavourable. He seems to have been especially pleased with some aspects of the character of the Mangbattus, his observation of whom enabled him to say that the "tender side' of negro feeling had been called in question unjustly. The women of this tribe hold a relatively high position. They are allowed to take part with the men in public gatherings, and some of them were occasionally able to act as Dr. Junker's interpreters. The Mangbattus have a decidedly artistic faculty, which they display most effectively in the making of iron weapons. They have a kind of knife which seemed to Dr. Junker "unsurpassed for the beauty and originality of its numerous forms"; and their spear-heads "present an amazing variety of types in the size and shape of the barbs, teeth, and tips." They also "display surprising technical skill in the artistic

treatment of diverse wooden utensils and earthenware vessels, which, as in all these negro lands, are turned out without the aid of the potter's wheel." Dr. Junker's geographical observations relate to a comparatively small area, but their thoroughness gives them a unique place in the literature of African exploration; and naturalists will read with interest everything he has to say about the flora and fauna of the districts he traversed.

Scientifically, Major Wissmann's book is of less importance than Dr. Junker's. It records his experiences. during his second journey through Africa, which was undertaken in 1886, when he was still in the service of the King of the Belgians. His instructions were to open various parts of the interior of the Congo State; to investigate, and, as far as possible, counteract, the proceedings of slave-hunters; and to report on the countries bordering the Congo State towards the south-east. He made in the first instance for the Bashilange country, where he re mained for some time, exploring the region and settling various political affairs. In November he left Luluaburg at the head of a caravan consisting of 900 persons, who accompanied him eastward to the neighbourhood of Nyangwe, on the Upper Congo, whence they were taken back to their native country by Lieutenant Le Marinel, At Nyangwe Major Wissmann was detained by Zefu, Tippu Tib's son, but ultimately he was allowed to depart, and reached the east coast by Lakes Tanganyika and Nyassa, and the River Shire.

The most important parts of the work are those relating to the outrages committed by the infamous slavehunters; but there are also a good many valuable passages in which the author embodies the results of ethnographical study. Among other peoples described by him are the dwarfs whom he met in the primæval forest. They reminded him of portraits he had seen of Bushmen. They were " of a brown-yellowish colour, or rather light yellow, with a brown shadowing." Their demeanour was "timidly modest," and he had to be careful not to touch them, as they were always ready to take to their heels. An agreeable impression was made by the rounded figures, fresh complexions, and graceful, easy, quiet movements of the young, but the old "might literally be called painfully

with intellects so shattered that, instead of taking their places in the front rank of English statesmen, as their abilities entitled them to do, they sought rest for their brains in the quiet lives of country gentlemen. In my own modest sphere, I well remember the refreshment occasionally derived from five minutes' sleep on a deal table, with Babbage and Callet's Logarithms' under my head for a pillow."

Millennium. The letters C. of M.,' Commencement of work of the house." Millennium, were actually inserted in flint in the brick

Having saved some two or three hundred pounds, he went with Frankland in 1848 to study science in Germany, and selected Marburg as a place where he could live cheaply amid agreeable surroundings. Here, if the mists of intervening years have not unduly magnified the past, we must believe that he worked without weariness for sixteen hours a day. There were about three hundred students. Bunsen was the Professor of Chemistry, and appears to have given great prominence to chemical physics. His lectures included the electric telegraph, and a very full exposition of Ohm's law; and in the

New England.

The lecture on Thomas Young contains a vivid de

lineation of his personal qualities, and, besides tracing his achievements in physical science, gives a very clear and intelligible account of the methods by which he succeeded in deciphering the Egyptian hieroglyphics. In the accompanying narrative, his openness and plain dealing are strongly contrasted with the crafty suppressions of his rival, Champollion, who, being a professional antiquarian, appears to have thought it intolerable that he should be beaten in his own special province by an outsider.

To many readers, the most interesting portions of the "Fragments" will be those which are autobiographic.

An address, delivered at the Birkbeck Institution in 1884, contains a sketch of Prof. Tyndall's early career, first as a draughtsman in the Ordnance Survey, then as an Ordnance surveyor in the field, next as a railway surveyor in the rush of work which sprung from the "railway mania." Here is a specimen of his recollections of that date:

Among the legal giants of those days, Austin and Talbot stood supreme. There was something grand, as well as merciless, in the power wielded by those men in entangling and ruining a hostile witness; and yet it often seemed to me that a clear-headed fellow, who had the coolness, honesty, and courage not to go beyond his knowledge, might have foiled both of them. Then we had the giants of the civil engineers-Stephenson, Brunel, Locke, Hawkshaw, and others. Judged by his power of fence, his promptness in calculation, and his general readiness of retort, George Bidder as a witness was unrivalled. I have seen him take the breath out of Talbot himself before a Committee of the House of Lords. Strong men were broken down by the strain and labour of that arduous time. Many pushed through, and are still amongst us in robust vigour. But some collapsed; while others retired with large fortunes it is true, but

to Joule.

In process of time our student began to make original investigations, and his first paper was on the phenomena

of water-jets. It included the remark that the musical sound of cascades and rippling streams, as well as the due to the breaking of air bladders entangled in the sonorous voice of the ocean, was mainly if not wholly

water.

After taking his degree at Marburg, he came over to England, but soon returned with his friend the late Prof. Hirst to Germany, where he studied at Berlin under Magnus, and met Dove, Ehrenberg, Mitscherlich, Du Bois-Reymond, Wiedemann, Clausius, Poggendorff, and Humboldt.

The happy associations of University life strengthened many, and he professes great admiration for the German the predilections which originally attracted him to Ger

character, which, alike in science and in war, aims not at

glory, but at the discharge of duty.

Further gossip of an autobiographical kind is furnished under the head of "Old Alpine Jottings," which occupy the last seventy pages of the volume. Here we find him recruiting exhausted nature, after intellectual toil, by arduous climbing on icy slopes, over fearful precipices, and under a fusillade of boulders shooting down from the heights above.

Perhaps the most vigorous piece of writing in the book is that which is placed first-a lecture on Sabbath observance, delivered in 1880 before the Glasgow Sunday Society; and we must not omit to mention the second article, which gives a very full account of Goethe's work on colour. It pays a high tribute to Goethe's acuteness as an observer, but gives an unsparing exposure of his weakness as a scientific theorist.

The volume, though not ambitious, contains much pleasant reading. J. D. E.

OUR BOOK SHELF.

A Treatise on Chemistry. By Sir H. E. Roscoe, F.R.S., and C. Schorlemmer, F.R.S. Vol. III. "The Chemistry of the Hydrocarbons and their Derivatives; or, Organic Chemistry." Part VI. (London: Macmillan and Co., 1892.)

THE present section of this well-known work deals with the derivatives of naphthalene and the allied hydrocarbons -phenanthrene, chrysene, &c.; also with the compounds containing two or more benzene nuclei directly united, such as diphenyl.

The extraordinary expansion which this particular branch of organic chemistry has undergone during the last fifteen years is due in part doubtless to the fascination of the various problems of constitution which these compounds offer, and to the well-founded assurance that Kekule's benzene theory, which had thrown so much light on the subject of benzene itself and its more immediate derivatives, would prove an equally trustworthy guide in the case of the more complex hydrocarbons of the same class. But it is doing no injustice to pure chemists to say that a great part of this expansion is attributable to the fact that numerous valuable practical applications have been found for some of the compounds in question.

In 1876, when Wurtz published his "Progrès de l'Industrie des Matières Colorantes Artificielles," the colouringmatters derived from naphthalene might be counted on the fingers of one hand, and not more than two of theseMagdala red and Manchester yellow-were really manufactured; whilst from diphenyl not a single dye-stuff had been prepared. At the present moment, only a specialist in this branch could estimate, even approximately, the number of the naphthalene dyes; and within the last few years another important class of dyes, possessing the hitherto unknown property of dyeing cotton without a mordant, has been discovered among the derivatives of diphenyl.

The industrial source of much of our knowledge in this branch of chemistry is clearly shown in the fact that in the work now before us the references are not confined to the

familiar scientific periodicals, but extend to the patent literature of various countries and to works like Schultz's

"Steinkohlentheer" and Friedländer's "Theerfarben." Without going into unnecessary detail, the authors succeed in giving all which it is necessary for the student of organic chemistry to know regarding these matters.

The questions of constitution are treated very fully and clearly. The reader who wishes to gain an idea of what organic chemists have accomplished, in the solution of problems which but a few years ago would have been regarded as utterly beyond the scope of rational investigation, cannot do better than study carefully the chapter on the constitution of the naphthalene derivatives.

The authors continue to follow their excellent practice of giving interesting historical details by way of introduction to the study of the more important compounds. The Oak: a Popular Introduction to Forest Botany. By H. Marshall Ward, M.A., F.R.S., F.L.S. "Modern Science Series," edited by Sir John Lubbock, Bart., M.P. 171 pages, and Index, 2 Plates, and 51 Woodcuts. (London: Kegan Paul, Trench, Trübner, and Co., Ltd., 1892.)

THIS little book fills a distinct gap, as it is the first time that a primer intended specially for students of forestry has been issued in England. Prof. Marshall Ward has been for many years the Lecturer on Botany at the Royal Indian Engineering College at Cooper's Hill, and therefore understands thoroughly what is required. He has followed for his plan the taking of a single tree-the oak

and dealing with it exhaustively. After a general introduction, he deals first with the acorn and its germination, describing fully the embryo and its epidermis, the vascular bundles of the former and its cells, and the character of their contents. He tells us that two years

elapse before the supply of food stored up in the two thick cotyledons is exhausted, and it is not until the tree is from sixty to a hundred years old that good seeds are obtained from it. Then he describes the seedling and young plant-first the root and its tissues, and then the stem, buds, and leaves, and their microscopic structure. Then he turns to the full-grown tree, and describes its root-system, shoot-system, inflorescence, flowers, fruit, and seed. Next he deals with the timber of the oak, its structure, and technological peculiarities. Then he treats of the cultivation of the tree, and the injuries and diseases to which it is liable from the attacks of insects and fungi. He concludes with a short chapter on the relationships of the oaks and their distribution in space and time. the acorn is inclosed, which represents a one-flowered The genus is characterized by the cupule, in which involucre. There are three cells in the ovary, and two ovules in each; but nearly always two of the cells and five of the ovules are obliterated before the seed is perfected. About 300 species of the genus Quercus are known. It is spread universally through the north temperate zone. Prof. M. Ward is mistaken in supposing there are no oaks in South America. Two species have long been known in the Northern AndesQuercus tolimensis and Quercus Humboldtii-both of which are described and figured in Humboldt and Bonpland's "Plantes Equinoxiales." There are nearly sixty species in India, and it is there that we get the genus connected with the other Cupuliferæ by passing through Castanopsis into Castanea. The oaks go back to the Cretaceous period, and a large number of fossil forms are known. Their delimitation into species is very difficult. In Britain we have only a single species, Quercus Robur, with two sub-species Q. pedunculata and sessiliflora, well enough marked in their extreme forms, but

passing into one another by gradual stages of transition, which constitute what has been called Quercus intermedia. The book is clear and well arranged, and will be found thoroughly adapted to fulfil its purpose, and is illustrated by a large number of excellent figures, some of which are original and some borrowed from German text-books. J. G. B.

The Elements of Plane Trigonometry. By R. Levett and C. Davison. (London: Macmillan, 1892.) THOUGH the spirit of De Morgan's writings pervades these "Elements," there is ample evidence that the writers have taken an immense amount of pains in bringing them fully up to date. We have long given up looking for originality in a treatise on trigonometry; indeed, in a text-book for use in schools such a feature is hardly desirable, but there are not wanting here many novel features in the matter introduced and in its mode of treat

ment. De Morgan's influence is shown "in the use of the negative hypotenuse in defining the ratios, in the more functions, the manner in which the addition formulæ are definite meaning assigned to the notation for inverse treatment of the hyperbolic function and of complex extended to any number of variables, the geometrical numbers, and in the two-fold generalization of a logarithm to a given base." Another work to which the authors are indebted in Parts II. and III. is Prof. Chrystal's masterly treatise on algebra. In fact, they are au courant with whatever has recently been written bearing in any way upon their subject-matter.

The book is divided, like ancient Gaul, into three parts. The first treats of arithmetical quantity, in five

chapters; the second of real algebraical quantity; and the third of complex numbers. The first two parts contain what is requisite for school use, the third is beyond the ordinary run of junior students. The whole has, we believe, stood the test of class work. In the second part the application of trigonometry to surveying is made interesting by treating the subject as practically as possible. There is a copy from a photograph of a theodolite, and a conversational description of the same, and in Part I., through the permission of the publishers, there is printed a portion of the map of the Mer de Glace given in the "Life of Prof. Forbes." These little points are likely to interest young students. Of course the hyperbolic functions are discussed, but they are discussed in a way that is novel to us in some of the details; for instance, geometrical proofs are given of cosh (u + v) and sinh (u + v). These strike us as being very elegant and quite within school range, as they need only a moderate acquaintance with the properties of the rectangular hyperbola. A short space is occupied with the Gudermannian function, and a table of approximate values of hyperbolic functions is given in the same section. The section on convergency and continuity of series, and, in fact, the whole discussion of series, is very carefully done.

Our summing up is that the book is one of the best we have met with on the subject, and quite fitted to hold its own against the two or three formidable rivals that have lately appeared in the field. There is a plethora of carefully chosen examples, which we advise the junior student to use with Prof. Chrystal's caution in mind: "I should much deprecate the idea that any one pupil is to work all the exercises (in the 'Algebra ') at the first or at any reading. We do too much of that kind of work in this country.' The text is further illustrated by many graphs of different functions, and answers, carefully tested from working with pupils, are appended at the end, with tables of the logarithms required for the exercises.

Les Fleurs à Paris: Culture et Commerce. Par Philippe L. de Vilmorin. (Paris: J. B. Baillière et Fils, 1892.) THE trade in cut flowers is now quite an important department of commerce, and it is rather surprising that a good many attempts have not been made to give a full and connected account of it. In the present volume M. de Vilmorin deals with the subject chiefly in its relation to Paris, and he has brought together many facts which will be of interest both to lovers of flowers and to students of social economy. He describes the various ways in which the trade is organized in the French capital, the sources from which the flowers are derived, the manner in which they are cultivated, and the means by which they are distributed. He then presents an account of the various kinds of flowers used for decorative purposes, giving in simple language such botanical details as are likely to be intelligible and attractive even to non-scientific readers. The volume is abundantly and very prettily

illustrated.

Health Springs of Germany and Austria. By F. O' Buckland, M.D. Second Edition. (London: W. H. Allen and Co., 1892.)

THIS little book ought to be of considerable service to invalias who may desire to obtain aid in the choice of a Continental health resort. The author does not profess to present elaborate details as to the various springs with which he deals; but he says enough about each to give a sufficiently clear idea of its merits and defects. He offers also some good general remarks on the nature and uses of health springs. In the present edition he has made little change, but he has increased the value of the book by adding an index.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.]

Heat Engines and Saline Solutions.

above heading (p. 438); but to deal completely with all the I HAVE nothing to modify in what I have written under the questions raised by Mr. Macfarlane Gray (p. 486) would require half a treatise. I will limit myself to a few brief remarks. (1) In Carnot's engine there is no (separate) boiler or condenser.

(2) When I spoke of the various parts of the working substance being in equilibrium with one another, I referred to complete equilibrium, thermal as well as mechanical. If the temperature varies from one part to another there is no equilibrium. (3) On the above understanding the pressure of vapour in equilibrium with a saline solution of given strength is a definite function of the temperature.

(4) Let me suggest that the origin of the difficulty may lie in the phrase "superheated vapour," which has not so definite a meaning as Mr. Gray seems to ascribe to it. Whether vapour be superheated or no, depends, not only upon the condition of the vapour itself, but also upon the bodies with which it is in contact. Vapour which is merely saturated in contact with a saline solution must be regarded as superheated when contact with the solution is cut off. In the first situation it would condense upon compression, and in the second situation it would

not.

IT seems that the earth, once set in vibration, maintains this state for a long time before coming to rest. The observers of Greenwich (see Major H. S. Palmer in the Transactions of the Seismological Society of Japan, vol. iii., p. 148) found that from time to time, at considerable intervals, there was an evening when the usual observations for determining the collimation-error of the transit-circle by means of reflection in a tray of account of the constant mercury could not be taken, on trembling of the surface of the mercury, which on such occasions continued until long past midnight. These are occasions when crowds of the poorer classes of London flock for amusement to Greenwich Park. A favourite pastime with the young people, often prolonged until after nightfall, is to clamber to the top of the steep slopes of the hill on which the Observatory stands-in fact, to the paling of the enclosure—and then, joining hands in twos or threes, to bolt precipitately to the bottom, where, as may be imagined, they usually arrive "all in a heap." Hundreds join in this sport on fine evenings, and the result, as shown by the behaviour of the mercury, is to set the whole of Flamsteed Hill in a tremor, which does not subside until early next morning, many hours after the people have left.

Another very beautiful proof of this fact offered itself to me in the Geophysical Observatory of Rocca di Papa, Rome. A slight earthquake coming from Aquila (at 110 kilometres north-east of Rocca di Papa) was felt and registered by the instruments at 9.39 a.m. mean time of Rome, on the 8th of last February. Just at that time I was casually observing through a microscope a pendulum 6 cm. long, which suddenly began to display grea: agitation.

position for an amplitude equal to the observed, comes to rest Now such a pendulum, when removed from its equilibrium in about half-an-hour. In the present case the pendulum con tinued to oscillate till the afternoon. Nor did the character of the vibrations correspond to the gradually and regularly diminishing oscillation of a pendulum which has received a single shock The pendulum is firmly fixed to a big column, deeply founded