of harmonic analysers, including those of Henrici, and the machine devised by Michelson and Stratton for their analysis of visibility curves of interference fringes.

The information given in the book seems, on the whole, fairly complete and accurate. The word “periode" seems used in a loose sense, sometimes as "time of a single oscillation" and sometimes as "frequency." J. A. HARKER.

a

Cultures du Midi de l'Algérie et de la Tunisie. By C. Rivière and H. Lecq. Pp. xii+511. (Paris: J. B. Baillière et Fils, 1906.) Price 5 francs. In view of the fact that inside the British Empire agriculture is being practised under all sorts of tropical and semi-tropical conditions, there is singular paucity of books in the English language dealing with the cultivation of exotic plants. The book before us, one of the "Encyclopédie agricole series, reviews briefly the whole range of plants which are cultivated economically in the Mediterranean region belonging to France, i.c. in Provence, Algeria, and Tunis. This is a very special district possessing a characteristic flora adapted to its well-marked climatic conditions of insufficient rainfall which falls mainly in the winter, great heat and dryness in the summer, excessive radiation resulting in extreme variations of temperature, with sharp frosts in the winter, incessant wind, and an all-pervading sun. Under these conditions many forms of agriculture are only possible where irrigation water is obtainable, and much of the country is little better than bare rock or sand; there are, however, many im. portant cultures, special to the district, which have been brought to a high state of perfection by the inhabitants of the Côte d'Azur.

The most distinctive example is perhaps the growth of plants for scent and essences which has its centre at Grasse, but which has been extended into both Algeria and Tunis; the rose, the orange-flower, the tuber rose, the violet, and the jasmine being the most important of the flowers thus cultivated. The olive, that most distinctive feature of all Mediterranean landscapes, is losing ground, we learn, being displaced by

the competition of oils like cotton-seed and sesame; in Provence, also, the land is wanted for more intensive forms of cultivation, such as the production of early vegetables and cut flowers.

The book of MM. Rivière and Lecq suffers somewhat from the very extensive ground it has to cover; the accounts of each plant in cultivation have to be so curtailed that the details are insufficient for the needs of the practical man, who will, however, find an excellent series of references to more special books and articles on each subject. The book may be of considerable service to many of our colonists living in semi-arid countries and looking round for suitable and remunerative crops to grow; from it they can obtain both ideas as to possible introductions and such economic information as to the labour required and the probable value of the returns as may enable them to embark on the experiment with some prospect of success.

Tabulae Botanicae. (Part i., containing plates i. and ii.) Edited by E. Baur and E. Jahn. (Berlin : Gebrüder Borntraeger, n.d.) Price per plate: paper, 7 marks; cloth, 10 marks. Series of five, 25 marks. UNDER this title the publishers announce a series of coloured illustrations of plants intended for lecture purposes, and arranged in sets for each subject, order, or class. The two diagrams received illustrate the Myxobacteriacea, the one representing Successive stages in the life-history of Polyangium fuscum, selected as a general type, the other depicting the fructification, spores, &c., of Myxococcus and

Chondromyces as special details. So far as one can judge from these specimens, the drawing entrusted to Ehrlich, of Berlin, promises to combine correct representation and artistic treatment, and the publisher's name is sufficient guarantee for good reproduction; the paper selected is not strong enough to withstand wear and tear, but at a somewhat higher price the plates may be obtained backed with linen and attached to rollers. The size of the diagrams, about 5 feet by 3 feet, is sufficiently large for most practical purposes. The short prospectus prefixed to the accompanying text provides little information, except to say that the plates will be designed two, three, or more to each subject, that the series will histories of plants, and that the lower plants will cover the whole field of the anatomy and the lifereceive especially full treatment.

Reports of the Expedition to the Congo, 1903-5. Liverpool School of Tropical Medicine, Memoir xviii. Pp. 74. (London: Williams and Norgate.) Price 7s. 6d. net.

In this report, the late Mr. Dutton and Dr. Todd contribute an important paper on gland-palpation in human trypanosomiasis, in which they show that most early cases of trypanosomiasis have enlarged glands, and can therefore be detected by gland-palpation. A second paper by the same authors discusses the distribution and spread of sleeping sickness in the Congo Free State. This is illustrated by four maps, which demonstrate very clearly the enormous extent of territory in which this terrible disease is now met with compared with twenty years ago. This is in great measure accounted for by the increase in travel following the opening up of the country. Two new Dermanyssid Acarids from monkeys' lungs are described by Mr. Newstead and Dr. Todd, and Dr. Stephens and Mr. Newstead contribute a paper on the anatomy of the proboscis of biting flies. It will thus be seen that the report contains matter of considerable interest, and the general "get up" leaves nothing to be desired.

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Ten Years' Record of the Treatment of Cancer without Operation. By Dr. Robert Bell. Pp. 107. (London: Dean and Son, Ltd., 1906.) Price 2s. 6d.

net.

IT is difficult to understand the raison d'être of this book, which consists mainly of a diatribe against the modern surgical treatment of cancer, and a veiled recommendation of the author's method of treatment by medicinal and hygienic measures. As regards any record" of ten years' treatment by the author's methods we find little evidence--" several cases' eventually got quite well (p. 42), a case "recovered completely (p. 43), a case in which "the tumour quite disappeared (p. 63), three cases in which recovery was complete (p. 71). This constitutes the "record"; can the author be surprised if his views and methods be received with scepticism?

R. T. H. The Opal Sea. By John C. Van Dyke. Pp. xvi+ 262. (London: T: Werner Laurie, 1906.) Price

6s. net.

PROF. VAN DYKE provides in these pages a readable account of many branches of modern oceanography expressed in a literary form too seldom found in works dealing with scientific subjects. As one would expect, the romance and poetry of science are given great prominence, and the attractive word-pictures reveal the fascinating nature of the work of the man of science. Many readers of these essays will be encouraged to undertake a more precise study of the physical geography of the sea from formal treatises.

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.]

The Stability of Submarines.

SIR WILLIAM WHITE, in his paper in the Roy. Soc. Proceedings (vol. lxxvii. A., p. 528), discusses the hydrostatic forces tending to stability or instability of a submarine at the surface of the water. When the vessel is in motion, hydrodynamical forces come into play from the stream-line action of the water, and these also will affect the stability of the vessel. Sir W. White insists that these forces can only be examined experimentally, and has no data to give as to their magnitude. Although it is obviously impossible to obtain an exact calculation of the magnitude of these hydrodynamical forces, yet it may be worth noticing that a very simple calculation will give an approximation to their value, which at least is of importance in that it suggests that the question is one of extreme gravity. The principle involved is, of course, the well-known principle by which an ellipsoid moving through still water tends to turn so that its smallest axis is in the direction of motion.

We may obtain a first approximation to the stream-line action by treating the submarine as a cigar-shaped spheroid, and assuming it to be completely immersed in an infinite ocean. Let a, b denote the semi-axes of the spheroid, and let it be moving with velocity V, its major axis making a small angle with the horizontal. The couple tending to decrease is known to be

Sir William White gives as the metacentric height of an actual submarine 37 feet when awash on an even keel, and only 45 per cent. of this, say 16 feet, when trimmed to an angle of 4 degrees. The value of VE when V10 knots, is about 9 feet, so that the effective metacentric height would be reduced to about 28 feet on an even keel, and to 7 feet when trimmed 4 degrees by the stern. So far as can be judged from a diagram given by Sir William White (Fig. 7 in his paper), the metacentric height would vanish altogether for a trim of about 7 degrees.

Thus a submarine moving ahead at 10 knots, even under perfect conditions, might apparently be expected to founder if its inclination at any time reached as much as 7 degrees. Sir William White mentions that in the case of the submarine A8, the hydrostatic metacentric height had been reduced, at the time the accident occurred, to 8} feet. The further diminution in this height produced by a headway of 8 knots is about 6 feet-by a headway of 9 knots is about 7 feet, leaving only about 1 foot of effective metacentric height as the margin of safety.

Obviously these rough calculations ignore a great number of factors which ought to be taken into account before accurate knowledge can be obtained. The most important of these factors is probably the proximity of the surface and the consequent formation of surface-waves. A calculation which omits a factor of this kind cannot lay claim to any value as advancing exact knowledge, but may serve the humbler purpose of suggesting possible, and even probable, dangers, and of emphasising the need for experimental knowledge, before this is forced on us by a catastrophe. J. H. JEANS.

Trinity College, Cambridge.

THE mathematical investigation which Mr. Jeans puts forward is of great interest, but avowedly rests on the assumption of the complete immersion of a submarine in an infinite ocean. The concluding paragraph of his letter indicates that a great number of factors, which ought to be taken into account, are not represented in the mathematical investigation, the most important being near proximity to the surface and the consequent formation of surface-waves. It will suffice, therefore, for me to say that my insistence on the necessity for direct experiment, rather than mathematical investigation, had relation to the case where the submarine was moving at the surface with a small reserve of buoyancy. The slides which I exhibited at the Royal Society reproduced photographs taken in these circumstances, and showed the singular and irregular character of the surface-waves produced by the headway of submarines under these conditions. These slides furnished conclusive evidence of the impossibility of representing the conditions of practice by purely mathematical investigation, and the absolute necessity for experiments on models and full-sized submarines.

Mr. Jeans's investigation for the completely submerged vessel has, however, a great practical value, because it furnishes fresh and important reasons (in addition to those urged by myself) against the tendency to increase the under-water speeds of submarines. When submerged, the clination is found in the height of the centre of buoyancy measure of stability of the vessel for all directions of inabove the centre of gravity. We are informed authori tatively that in the diving condition this height is less than

foot in existing types of submarines. It will be seen. therefore, that a very small value of V-less than 6 knots --might render such a vessel unstable; if the speed were increased to 10 knots no possible use of water-ballast could give such a hydrostatic stability to the vessel when at rest as would secure the maintenance of stability when she moved at full speed. The existence of superstructures on the upper portions of submarines, of course, involves a departure from the cigar-shaped spheroidal form, but cannot be accompanied by any such decrease in the moment of the couple resulting from the stream-line forces as would secure, or even add sensibly to, the safety of the submarine moving at high speed under water. W. H. WHITE.

The Action of "a" Radiation on Diamonds. THE action of the a rays" on diamonds is of considerable interest, for while the fluorescence caused by the B and radiation from radium is probably similar to that caused by the X-rays, the appearance of a diamond made luminous by the impact of a stream of "a" particles suggests some considerations as to the possible action of

radiation on fluorescent crystals in general. The fluorescence of a fairly large stone (cut and polished) when viewed with a suitable lens shows practically nothing of the spinthariscopic action, although the stone may be brightly luminous. Instead of the familiar scintillations, the whole crystal, or at least the whole surface exposed to the rays, appears to give out a steady bluish-white light.

The thought at once occurs to one that this seemingly continuous flow may be the collective effect of the very numerous scintillations produced by a too intense stream of "a" rays; such an action is well shown on a zinc sulphide screen when there is an excessive quantity of radium used. That this action is really the collective fluorescence of scintillations is at once evident by removing the fragment of radium to a greater distance, reducing the quantity used, or increasing the magnifying power employed to view the screen. In the case of a diamond, however, this does not appear to be so. The use of a higher power to view the fluorescence still shows a seemingly steady glow, and the increase of the distance between the radium and the stone merely causes the light to become gradually fainter, while still preserving its steady character. Yet it is certain that the diamond responds

64

readily to the "a" particles, and also that, as the quantity of radium is so very small, the action of the 8 and y radiation is quite negligible. It is, of course, well known that when an a" particle strikes a fluorescent screen, the point of impact becomes the centre of a luminous area, which is simply enormous in extent when compared with the size of the atomic projectile which causes it.

a

The following may perhaps be suggested as a possible explanation of this action :-When an α particle strikes a homogeneous fluorescent crystal (say a diamond), the energy which excites the fluorescence finds equal conduction in all directions. The fluorescence caused thus tends to fill the whole volume of the crystal. If there are many such atomic projectiles incident on the same crystal, they are all tending to do the same thing, and consequently their spheres of influence mingle with one another. As such spheres of fluorescence find equal conduction of all sides, they extend indefinitely within the limits of the crystal in question. As fluorescence is apparently molecular property, and probably electrical in its nature, it is not difficult to imagine that such may be the case. A still pond, into which a handful of gravel is scattered, may present an approximate analogy. The ring-waves (neglecting the time they take to travel) would mingle with one another, and yet each one might be said separately to occupy the whole area of the pond. In the case of a zinc sulphide screen, or one coated with minute fragments of diamond crystals, the energy received by one crystal or fragment of a crystal is confined exclusively to the volume of that fragment. Moreover, it is impossible for an particle to strike more than one crystalline fragment at a time, for it is a body of atomic dimensions compared with which the most minute fragment of the fluorescent compound would be enormous.

"a"

The whole of the available energy is thus confined to the limits of the fragment struck, and is not, apparently, extended to the neighbouring crystals, which are only in loose and indifferent contact with it. When such a crystalline fragment is of a size which is comfortably visible with the aid of a lens magnifying about 20 diameters to 30 diameters, the resulting fluorescence will be visible as a scintillation. To diminish the size of the crystals bevond a certain point in order to increase the brightness of the scintillations is apparently not advantageous, as it requires the higher powers of a compound microscope to render the areas properly visible, and there would be a corresponding loss of light.

On the analogy of the pond given above, the spinthariscopic effect may be compared to throwing a handful of

64

gravel into a collection of small puddles. The disturbance caused in each would be strictly confined to its own area, and would be correspondingly intense within that area. With a given stream of α radiation, a small stone appears to give a very slight scintillating effect which is not seen in a larger stone, except at the edges and angles of the facets, where the area of fluorescence is abruptly terminated, and even here it is very faint. The above remarks would, of course, only apply to perfect crystals. If a crystal is full of flaws and imperfections, the areas or spheres of fluorescence would not find easy conduction across the faults, and would therefore become localised in their action. It may be noted that a lump of willemite (natural), which is of a semi-crystalline character, does show scintillations, though very imperfectly, while the powdered mineral answers much better. This may be explained on the assumption that the areas of conduction are restricted to the size of the particles. C. W. R. June 20.

The Day of Week for any Date.

THE following method for finding the day of the week for any given date (new or Gregorian style) may interest your readers. We assign a number for each month in accordance with the old style, beginning with March, so that the last four months are numbered according to their Latin names, as follows:

January, o; February or March, 1; April, 2; May, 3; June, 4; July, 5; August, 6; September, 7; October, 8; next January, 11; November, 9; December, 10; February, 12.

next

For a Leap Year, January and February must count as II and 12 respectively in the preceding year.

It is only in dealing with the month-number that anything not straightforward and obvious is involved. The rule then runs as follows:

A. For the century: divide by 4, and calculate 5 times the remainder.

B. For the year: add to the number the quotient obtained from divisor 4.

C. For the month: multiply by 4, and negate the units digit (i.e. subtract instead of adding it).

D. For the day retain the number unchanged.

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SOME SCIENTIFIC CENTRES. VIII. THE MACDONALD PHYSICS BUILDING, MCGILL UNIVERSITY, MONTREAL.

WISE

ISE liberality has rarely reaped a richer and more immediate harvest than the gift by Sir William Macdonald of the Physics Building to McGill University at Montreal. This benefaction is but one instance though a very important instance--of the fact that education, particularly scientific and technical education, is of enormous practical advantage, and that the most wealthy men in Canada and the United States recognise that it has the first claim on their generosity. In England money is given with no less lavish hand, but vast sums are devoted to objects less deserving than education, inasmuch as they afford palliatives, and not preventives, of failure, suffering, or distress.

The Physics Building, with its accompanying endowments and equipment both for instruction and research, forms but a small fraction of the total gifts of Sir William Macdonald to McGill University-gifts which exceed in value three and a half million dollars. A brief history of its growth, more particularly as a centre of research work, may be of service to those desirous of emulating a noble example.

In 1891 a chair of physics was endowed by Sir William Macdonald, to which John Cox, formerly Fellow of Trinity College, Cambridge, was appointed as the first professor.. He was at once instructed to visit the best laboratories in America, and thus add to his experience of similar institutions in Europe. He received the most cordial assistance in the United States, and learnt both what to acquire and what to avoid. On his return, in conjunction with the architect, Mr. Andrew T. Taylor, he planned a building, beautiful in appearance, and so complete in every detail, that it is scarcely possible, with an intimate knowledge of the internal arrangements, to suggest any material improvements. The

income of 1500l. to provide for the salaries of demonstrators and to defray the cost of heat, light, upkeep of apparatus, and repairs to the fabric. As educational property is not subject to taxation in Canada, the only rate payable is the water tax. In addition to the preceding gifts, the donor of the Physics Building has made special grants from time to time for the purchase of radium, for a liquid-air plant, for two large induction coils, and in particular 1000l. for the purchase of books for the library in the building, and 400l. for a special research fund. It is fortunate that such splendid munificence has been judiciously expended by Prof. Cox, and that the results obtained have been such as to win for the laboratory a place in the foremost rank.

A detailed account of the rooms in the building is unnecessary, but an important item in the estab lishment is the workshop, with tools and lathes driven by electric motors, sufficient to make a large proportion of the more simple apparatus required for instruction or research. A complete plant of this

general scheme was to provide a building which would meet the requirements of the ensuing fifty years. The cost of the fabric was 29,000l., being at the rate of about elevenpence a cubic foot.

The donor further instructed Prof. Cox to prepare estimates for equipment and apparatus, and in response for a request of 5000l., the sum of 6000l. was placed at his disposal. At this point Sir William Macdonald decided to endow another chair for research in physics, and the institution was fortunate in obtaining H. L. Callendar, from Trinity College, Cambridge, as its first occupant. The equipment of the laboratory continued from 1892 to 1897, when the founder was assured that sufficient apparatus had been obtained; but the first grant had been greatly exceeded, and the total donation for this purpose was 22,000l. This sum has been discreetly spent, and adequate provision has been made for lecture tables, laboratories, and for all branches of physical research. Sir William Macdonald made a further gift of 30,000l. in order to secure an annual

nature, under a competent mechanic and assistant, effects a great saving of time and money in a city where skilled labour is often scarce and always costly. It is not within the scope of this article to give an account of the purely educational uses of this building, but it is sufficient to state that the lecture theatres and laboratories are ample in size and equipment, so that all students in the faculties of arts and of science receive courses in physics suited to the requirements of their future professions. An interesting question arises as to the extent to which professors of research should devote their time to the instruction of ordinary students. On the one hand, it may be regarded as a waste of valuable time. but from the student's point of view it is a great gain to come into contact, both in laboratory and lecture room, with the best intellects in his university. A research professor must necessarily devote some of his time to the instruction of advanced students, and particularly to the assistance of research students. It is therefore undesirable that any large

fraction of his time should be absorbed by giving lectures to elementary students. This difficult question of the division of time appears to have been satisfactorily solved in the Physics Building.

The first research professor, H. L. Callendar, was an active and able investigator. He invented and improved his platinum thermometer with an ingenious compensation method, and applied it to various uses. In conjunction with Prof. J. S. Nicholson, of the engineering building, he solved many temperature problems connected with the steam engine. He investigated some important meteorological questions, determining the temperature at various depths in the earth-a matter of special interest during the severe winters in Canada. He also constructed a self-record

heat of water at various temperatures. Dr. Barnes, with Dr. Coker, determined the effect of temperature on stream lines and the critical velocity. He has also made a close study of the properties and peculiarities of ice formation in Canadian rivers. Freezing does not occur merely at the surface, as in most English rivers, but, after passing rapids, water may congeal at the bottom and form "anchor ice." Still more remarkable is the formation of "frazil," consisting of minute crystals pervading the whole mass of water. The presence of ice in this state occasions serious trouble in the turbines of the power stations, and special precautions are necessary to mitigate the evil. On the appointment of Prof. Callendar to the chair

ing instrument which measured the difference of temperatures between the top of Mount Royal and the base near the observatory. Further results have been obtained by Prof. C. H. McLeod and Dr. H. T. Barnes, using the same instrument. The latter was also associated with Prof. Callendar in effecting some improvements in the Clark cell as a standard of electromotive force. But Prof. Callendar's most important work at McGill was the development, in conjunction with Dr. Barnes, of the continuous flow method of calorimetry. This has proved a great advance, both for simplicity and accuracy, on the older methods of calorimetry. Very exact determinations have thus been made by Dr. Barnes of the mechanical equivalent of heat, and of the specific

of physics at University College, London, Prof. Cox again visited the Cavendish Laboratory, and, on the advice of Prof. J. J. Thomson, he selected to fill the vacancy E. Rutherford, a young man who had already distinguished himself for originality, insight, and great capacity for work. Soon after M. Becquerel's discovery of the radiations from uranium, Rutherford had published a paper on that subject, and removed some misapprehensions as to the properties of the radiations. Moreover, he had served a most useful apprenticeship on the investigation of the properties of ions, whether produced by Röntgen rays, ultra-violet light, or by uranium. This thorough mastery of the indispensable elements served him in good stead when he continued at Montreal his