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ABNORMAL VARIABILITY OF MIRA CETI.-The variable o Ceti, or Mira, is perhaps the most interesting of all known variables, and its large range of magnitude, varying from a bright naked-eye star to invisibility, renders it an object of fascinating study. It is, however, a variable variable, for not only does its period of waxing and waning oscillate from about 320 to 370 days, but the brightnesses at maxima or minima do not always reach the same values. Sometimes the magnitudes reached at maxima are estimated to be from 1'2 to 3'9, and the minima magnitudes vary from 80 to 9'5. It is quite possible that these minor changes are themselves periodic. A note on the recent behaviour of this star is printed in the Memorie della Soc. degli Spett. Italiani (vol. iv., ser. 2, March), and in it Sig. A. Bemporad refers to the recent abnormal maximum. He points out that at the last maximum, which occurred in the present year, the variable only reached magnitude 4'2, while the previous maxima in 1919, 1911, and 1914 were 3'3, 3'5, and 3'6 respectively. Unfortunately, no data are given for the years 1912 and 1913, for it could then be seen whether there had been a gradual diminution of the brightness at maximum during those years. The values for the amplitudes (in magnitude) of the light waves, estimated from a minimum to a following maximum, are given by him as follows:

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and these values show a flattening out of the curve, especially during the last period. The intervals in days occupied from a minimum to the following maximum, for the same years as given above, were 118, 129, 122, 104, and these values again show the abnormality of the recent maximum.

Another communication on recent observations of this variable appears in Astronomische Nachrichten, N. 4801. This is contributed by Prof. A. A. Nijland, who gives a bright curve extending from July, 1914, to March of the present year. According to him, the minimum occurred on October 10 of last year and the maximum on January 29 of the present year, its magnitude not exceeding 40 with the naked eye on the latter occasion.

REPORT OF THE BOMBAY AND ALIBAG OBSErvatories. -The director of the Bombay and Alibag Observatories, Mr. N. A. F. Moos, presents his report on the conditions and proceedings of these observatories for the year ending December, 1914. As the work is chiefly routine, namely, time, meteorological, and magnetic observations, which vary little from year to year, the report is very similar to those of former years. It shows that the observatory has been free from plague or any other infection during the past year, although a severe epidemic raged in the town during the winter months up to the middle of May; that the time-balls were dropped successfully on almost every occasion; that the magnetic instruments are in good working order; that the Milne seismograph recorded forty-seven earthquakes during the year, one of which was a great disturbance (May 26), besides several small local and other movements, etc. A long list is given of the routine operations, and it is stated that the major portion of the volume of magnetic disturbances, charts, data, and discussion for the years 1906-14, which brings up to date the data, etc., published in the magnetic volume 1846-1905, is in the press, and expected to be completed shortly. The magnetic work in connection with the programme of the Australian Antarctic Expedition was completed during the year.

THE ANNUAL OF THE NATIONAL OBSERVATORY OF RIO DE JANEIRO.-The issue of the annual of the National Observatory of Rio de Janeiro is the thirty-first of the series, and, like its predecessors, contains a large amount of useful tables and data. The volume is divided into four parts, the first dealing with the calendar and astronomical data for the present year, the second composed of tables, etc., for the reduction of astronomical observations, the third giving a synopsis of the metric system, different units, and physical constants, and the fourth and last part concerning geo-physics and climatology, tables of the tides for numerous places forming an important portion of this section.

AGRICULTURAL RESEARCH AT THE ROTHAMSTED EXPERIMENTAL STATION.1 THE HE Rothamsted Experimental Station was for many years entirely supported by the generosity of its founder, the late Sir John Lawes, but latterly, as one of the institutes for agricultural research to which grants are made from the Development Fund, has been able considerably to extend the scope of its operations. Thanks to this assistance and to numerous private benefactions, the station has been able to enter into occupation of the Home Farm at Rothamsted, giving it scope for the desired increase in its field-work, and of a range of new laboratories, now nearing completion, that will compare favourably with those of any other institution of a similar nature. The day is past when a chemist alone could supply all the science an agricultural experiment station could be supposed to need; chemistry itself has become differentiated, and some of the agricultural problems demand the specialisation of an organic as others of a physical chemist over and above the purely analytical work that still constitutes so much of the routine of such a station. Biological questions are also involved, so that we see on the enlarged staff of the Rothamsted Station bacteriologists, botanists, and a protozoologist.

Dr. Russell, in recording the pulling down of the old laboratory wherein for sixty years so much of the pioneer work of the science has been accomplished, 1 Lawes Agricultural Trust. Rothamsted Experimental Station, Harpenden. Annual Report for 1914. (Harpenden: D. J. Jeffery, 1915.)

takes occasion to discuss the bearing of the work of a research station upon the development of agriculture. He maintains that its function is to obtain knowledge that the corps of teachers and experts now in the country can utilise. "Before the expert adviser and the teacher can do their work satisfactorily it is evident that definite systematic knowledge must be obtained of the subject with which they have to deal. Until this has been done much of their teaching must be purely conjectural, and may even be unsound-the history of the subject is full of illustrations in point. The only safe foundation on which their work can be built up is sound accurate knowledge gained by systematic investigation."

This appears to us very necessary doctrine; the State has now endowed Rothamsted so that it becomes subject to official criticism as to whether it is returning value for its money, and official criticism always likes to take its cue from the practical man. Yet much of the best work of Rothamsted must remain not merely unappreciated by, but unintelligible to, the practical man; the real test of its value must be whether it is moulding the opinion and rendering more accurate the advice of the teacher who is dealing directly with the farmer. To take a case in point: one of the commonest questions addressed to the scientific man by the farmer is whether he should lime his land, how much should be put on, and whether quicklime or carbonate. The first part of the question admitted of some sort of answer from analysis, though the chemist who began by determining the amount of calcium dissolved out of the soil by acid (a practice by no means extinct) arrived at most misleading results. Later the chemist began to determine the carbonate in the soil as a measure of the necessary base to supply which is the function of quicklime or carbonate, and latterly refined methods of analysis were devised to pick up the trace of carbonate which in many soils makes all the difference between fertility and poverty. Still, there were many dubious cases left; nor were they quite cleared up by attempts by means of litmus, etc., to determine whether the soil was neutral or acid.

In a set of papers abstracted in this report Hutchinson and MacLennan have practically cleared up the difficulties by attacking the problem from the chemical and biological side simultaneously. As an outcome they have devised an analytical process which proved sufficiently critical to indicate differences in the soil corresponding to the varying natural flora of parts of Harpenden Common, a non-calcareous soil verging on acidity and in places overpassing the neutral limit. These authors further were able to discriminate between the action of quicklime and carbonate of lime, so as to arrive at a rational explanation of the very different action upon the soil they occasionally exhibit. The continuous work these three papers represent would appear to a practical man to be wasted; he "knows" that lime is the remedy for sour soils and requires no research to teach him that. The shoe does not happen to be pinching him, but the time comes when some other practical man begins to wonder if his soil is sour and if he wants lime or had better try chalk or ground limestone, points on which the general maxim of sour soils requiring lime has no particular bearing So he turns to his scientific adviser, who is now, thanks to Hutchinson's and MacLennan's research, in a position to answer with some accuracy. We have laboured his point because it is typical; years and years of work of a research station, even if successful, may be required in order to modify a single sentence in a text-book, upon which, in its turn, depends the judgment of men whose function it is to advise the farmer.

To the practical man the work of a research station must always seem remote and in the air; fortunately the old field plots at Rothamsted have such an extraordinary fascination and raise such interest in the least scientific of farmers that the value of the unseen laboratory work has been also taken for granted; moreover, the new land available is being utilised for sundry temporary experiments of immediate interest to the working agriculturist.

PRESENTATION TO SIR PHILIP MAGNUS.

A DISTINGUISHED company assembled in Car

penters' Hall, London Wall, on Wednesday, June 2, on the occasion of the presentation to Sir Philip Magnus, M.P., of an address on his retirement from his position as superintendent of the technological examinations of the City and Guilds of London Institute, which he has held for the last thirty-five years, by the Association of Technical Institutions, a body representing more than ninety such institutions in the United Kingdom and in the colonies. The assembly was a fine testimony of the esteem in which he is held by all ranks of educationists for the eminent service he has rendered by speech and writings and by administrative work during a long and strenuous life. There were present, among many others, Sir Alfred Keogh, who presided, Sir Henry Miers, the Rt. Hon. Herbert Samuel, M.P., Mr. Pike Pease, M.P., the Rt. Hon. Sir Wm. Mather, Sir H. F. Hibbert, M.P., Sir Swire Smith, Sir George R. Kenrick, Sir Amherst Selby-Bigge, Sir John Struthers, Mr. Morton Latham, Prof. H. E. Armstrong, Dr. G. T. Beilby, and representatives of the Teachers' Registration Council, of the associations of directors and secretaries for education, of teachers in technical institutions, of the art masters, of Local Government officers, and of the College of Preceptors. The presentation of the illuminated address was made by Mr. J. H. Reynolds, and of the personal gifts to Sir Philip and Lady Magnus by Sir Wm. Mather. The address set forth the high appreciation of the association for the great services rendered by Sir Philip Magnus as a member of the Royal Commission on Technical Education of 1882, and for the important share which he has taken, not only in the development of technical education as a consequence thereof, but in the endeavour to place upon a sound footing the teaching of science in the secondary school and to introduce the principles and practice of manual training in all types of schools.

Reference was made in the course of the proceedings to the great value of the work accomplished by the institute under the guidance and inspiration of Sir Philip Magnus, to the help and encouragement given in the foundation of many technical institutions, to the establishment of a system of technological examinations which last year comprised seventy-three subjects attended by 56,000 students, and to the paramount necessity of more serious attention being given to the cultivation of science and to its application to industrial uses if the nation is to maintain successfully its industrial and commercial position in competition with other nations and especially with Germany. No attempts to "capture" German trade can have any possible chance of success unless they are founded on the sure basis of scientific research carried out by men thoroughly trained as scientific investigators, supported, as in Germany, by ample resources; and for this purpose it is necessary that there should be an entire change in the attitude of the English employer, from whom much more active encouragement and sympathy are needed. The course of the war has shown the enormous advantage which Germany enjoys as a result of her sedulous cultiva

tion of science in its technical applications, and the peril in which some of our staple industries have been placed by reason of our lack of dyestuffs and other materials which are the product of her great chemical manufactories, and which could, if proper encouragement were given and suitable measures taken, be produced in this country.

THE UNIVERSITIES AND INVESTIGATION.

MOST of us are perhaps a little tired of addresses

by eminent people explaining that the extension rather than the propagation of knowledge should be the primary object of a university. But the most jaded appetite will find something stimulating in a founder's day address delivered at Clark University by Prof. Ralph S. Lillie (Science, April 16). Nowhere has the case been put more simply and directly, with greater force and less of the overstatement which is apt to defeat its own objects; nowhere has the defence of useless knowledge' been conducted with greater cogency and sanity.

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But Dr. Lillie's main object is not to establish principles to which everyone in these days pays at least lip-service, but to inquire how best they may be put into operation. What exactly should a university do to encourage research? Build laboratories, endow chairs, and try to attract the best men to fill themsuch is the answer which would probably be given in this country. But American experience seems to show that something further is also needed. These things have been done on an unprecedented scale, and yet the production of work of the highest class is inconsiderable compared with that of several European countries far less lavishly equipped. Why? asks Dr. Lillie.

His answer is that the right spirit of research is lacking. He thinks that it has been too hastily assumed that the methods which have proved successful in the production of goods must be equally successful in the production of thought. The cult of the card-index, the typewriter, and the timekeeper has been carried too far; the heads of departments are overburdened with executive duties, and the demand for an appearance of strenuous activity leaves them and their subordinates no time to think.

And Dr. Lillie has a graver charge to bring. He accuses some American universities of being under the influence of a mistaken conception of democratic equality. He finds it necessary to protest against “a spirit of hostility to distinction." He quotes influential speakers to show that there is a tendency to underrate the importance of the exceptional mind and to imagine that everything can be achieved by industry without genius. He does not doubt the value of organised collaboration in the development of an investigation, but he fears that the exaggerated importance attributed to "team-methods" is apt to smother the individual inspiration from which all investigation must spring. "A university should be the stronghold of individuality," he protests in a notable phrase.

How far the diagnosis is correct it is not for a foreigner to judge, but the questions he raises have an interest beyond any immediate application. Is it really possible to do anything actively to encourage research? Will not official attempts to encourage the highest form of scientific learning have the same deadening effect as official attempts to encourage art? Can we do anything to produce a genius except avoid crushing him when he appears, and is even this negative precaution necessary? A genius is one who

moulds and is not moulded by his circumstances, and, in spite of Dr. Lillie's fears, the men he wants will appear in the fulness of time when they are ready.

MR.

N. R. Č.

ECONOMIC GEOLOGY OF NAVANAGAR.1 R. E. HOWARD ADYE, as Director of the Geological Survey of Navánagar, has written a memoir of 262 pages on the economic geology of the State. A coloured lithological map, on the scale of one inch to four miles, is bound up in sections with the volume, and numerous photographic plates of rocksections and a few landscapes illustrate the text. The rock-slices have been selected with the care that might be expected from Mr. Adye's previous work (see NATURE, vol. lxxvii., p. 125), and a system of lettering indicates the various mineral constituents. The production of this handsome and well-bound memoir by the Government of a native State in India renders the portrait of the Maharaja, Jam Shri Ranjitsinhji, distinctly welcome as a frontispiece.

One of the most interesting features of the region is the wide development of a foraminiferal limestone, which was laid down apparently in post-Pliocene times, and which is now in places 1100 ft. above the sea. The name "Miliolite" has been unfortunately given to this stone, and is retained, with suitable explanations (pp. 133 and 135), by the author. The rock becomes hard and durable on exposure, and has been used with marked success for building. Great masses of "hypabyssal" acid rocks occur in the south of the State, giving rise to the bold features of the Alech and Bard Hills. Mr. Adye predicts a commercial future for the micropegmatitic and other finegrained types (granophyres and felsites), which are capable of being highly polished, and are also serviceable as road-metal (p. 219). This series, with which a few rhyolites are associated, was intruded about the opening of the Eocene period into the widely-spread basalts of the Deccan trap. Pipe-amygdaloids (p. 56) and other types of the vesicular basic lavas are described. In dealing (p. 194) with the quality of toughness which characterises ophitic basalts, the nodular crystals of pyroxene in which the felspars are embedded are styled "plates." This is a very common slip, due to the impression given by these objects in rock-slices; but it injures the explanation given of the resisting properties of the rock. Perhaps we must not grumble at the new names proposed for altered limestones, "pindáralite" (pp. 178 and 181) for a marine rock permeated by iron hydroxide, and "ramwaralite" (p. 183) for a similar rock in which dolomite has developed. Such terms will at any rate attract interest within the State, and will thus serve one of the main objects of the book.

66

Mr. Adye's style has become curiously assimilated to that of certain Indian writers of English. Apart from the irregular distribution of commas, there are phrases like sacerdotal equipments" and revenons à nos moutons," and the statement (p. 9) that a range of hills has hitherto remained without a local habitation and a name,'" which would make a stranger doubt the author's nationality. How did a hill escape a local habitation? These things, however, probably show the influence of environment on a writer who is obviously throwing his energies into the development of the country which he serves.

G. A. J. C.

1 "Memoir on the Economic Geology of Navánagar State in the Province of Kathiawár, India." By E. H. Adye. (Pombay: Thacker and Co., 1914.)

THE

THE ROYAL OBSERVATORY,

GREENWICH.1

HE Moon's Tabular Place. The total number of observations made of the moon during the year ending May 10, 1915, is 107 with the transit-circle and 98 with the altazimuth, viz. :-64 in the meridian and 34 extra-meridian. Taking both instruments, observations of the moon have been obtained on 127 days during the year.

The mean error in right ascension of the moon's tabular place for 1914 is -0.876s. from meridian observations and -0.933s. from extra-meridian observations of the moon's limb, and -0.915s. from meridian observations of the crater Mösting A. The transit circle gives-o-899s. Attention is directed to the great increase in recent years of the mean tabular error of the moon's longitude. From 1883, when Newcomb's Empirical Correction was introduced into the "Nautical Almanac," the values (all reduced to the same equinox) are—

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- 11.93

- 13.0 Cookson Floating Zenith-Telescope.-During the year 238 photographs have been taken, 231 for latitude groups and 7 for scale determination. From the commencement of the observations, 1911, September 7, 609 latitude plates (excluding rejected plates) have been obtained, of which 553 have been measured in the direct, and 549 in the reversed position. In addition, 24 plates taken for scale have been measured and one plate rejected.

The results obtained since the commencement of the seven years' series of observations until the end of 1914 have been discussed, and the results communicated to the Royal Astronomical Society. The value of the aberration constant obtained is 20-467" ±0.006". The observations also furnish a determination of the latitude variation, although not designed primarily for this purpose. The latitude variation derived in this way shows a satisfactory agreement with the results of the International Latitude Service, and it is hoped that a comparison of the two series of results when the Cookson results have been brought to a conclusion will throw some light upon the origin of the z term in the latitude variation.

The 28-in. Refractor.-Observations of double stars have been made from a working catalogue containing all known double stars showing appreciable relative motion, which are within the range of declination of the instrument. A number of other stars are included for various reasons, particularly some of those discovered by Hussey and Aitken under 2" separation. Since October 16 M. Jonckheere, the director of the Lille Observatory, has also had the use of the instrument in connection with the catalogue he is preparing of double stars of less than 5" separation discovered 1 From the report of the Astronomer Royal, Sir F. W. Dyson, F.R.S.. to the Board of Visitors of the Roval Observatory, Greenwich. Read at the Annual Visitation of the Royal Observatory, on June 5.

since 1905, the date of Burnham's General Catalogue, and has carried out many re-measures and verification of positions.

Thompson Equatorial.-The work with this instrument has been concentrated on stellar parallax and photographic photometry. The photographs have all been taken with the 26-in. refractor.

The programme of stars the parallaxes of which are being determined contains all those between declination + 64° and the north pole which are known to have a proper motion of more than 20" a century. Each star is photographed at times of opposite parallactic displacement in right ascension on the same plate. It is found that six such plates give a good determina. tion. For three of the plates the first exposure is given when the star transits soon after sunset and the second exposure when it transits a little before sunrise, and for the other three the morning exposures are made first. Generally, the series of exposures will be extended over two or possibly three years, so as to avoid anything systematic in observational or instrumental conditions.

During the year ended May 10, a first exposure has been given to 238 plates and a re-exposure to 294. In the same period 234 plates have been measured and 39 in duplicate. Experience seems to show that duplicate measurement is unnecessary, it being understood that each plate contains six images of each star, three at each epoch, and that in the first measurement the plates are reversed and every image measured twice. the parallaxes of 40 stars have been determined, with an average probable error of ±0.009", and the results will be communicated to the Royal Astronomical Society.

The determinations of photographic magnitudes with the 26-in. refractor have been made by comparing certain fields with the polar standards determined by Prof. Pickering. Generally, exposures of 6 minutes have been made on Ilford "Monarch" plates, and the limiting magnitude reached is about 14-om. on the Harvard scale. During the year 88 photographs of this kind have been taken of the " selected areas" of Prof. Kapteyn.

Six-inch Astrographic Triplet.-The catalogue of photographic magnitude of stars down to the 9th magnitude between dec. +75° and +65° has been completed and published. It contains 5514 stars the magnitudes of which are determined with an average probable error of ±0.06m. The large field of this lens makes it very suitable for the determination of the photographic magnitudes of the brighter stars, and it is hoped to carry on this work in other declinations as opportunity offers.

Astrographic Equatorial.-The observing has consisted mainly of chart plates for the Oxford zone dec. +25° to +31°. Two exposures of 30 minutes each are given to each field, Wellington Xtreme" plates being used on account of their speed.

The printing of vol. iii. of the Astrographic Catalogue was finished in August. This volume contains the right ascensions and declinations, as well as the photographic magnitudes, of 16,780 stars from declination +64 to the north pole deduced from the measurements of the astrographic plates.

A thorough examination of these stars for the determination of proper motion is being carried out, and in addition to the catalogues mentioned comparisons are being made with the observations of Lalande, Argelander, and others. Proper motions have been determined for the stars of Carrington's Catalogue (dec. 81° to the pole), of the Kasan Catalogue (dec. 75° to So°), and of the Dorpat Catalogue (dec. 70° to 75°) as far as 18h. In a number of cases large proper motions have been verified by comparison of

plates taken at an interval of from 15 to 20 years. The largest proper motion found by this examination is 10 annually belonging to B. D. 77°, 361, a star of 9.2m. visual and 10-9m. photographic magnitude.

Heliographic Observations.-In the year ended May 10, photographs of the sun were obtained on 239 days.

The mean daily spotted area of the sun was 140 millionths of the sun's visible hemisphere during 1914, as against 8 in 1913, 37 in 1912, and 64 in 1911, thus showing the usual rapid rise from minimum.

Magnetic Observations.—The mean values of the magnetic elements for 1914 and three previous years are as follows:

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from the Eiffel tower have been regularly observed by Mr. Lewis and Mr. Bowyer. The mean of the times as observed by Mr. Lewis is +0.026s. late on Greenwich time from 209 observations, and by Mr. Bowyer +0.043s. late from 280 observations. The difference of a quarter of a second between the Eiffel Tower signal and the time as determined by the transit circle which existed two years ago appears to have been the personal equation of the standard observer as compared with the new impersonal micrometer.

The accuracy of the time-balls at the Admiralty signal stations and of the Westminster clock is shown by the following table of the errors of the returnsignals received at Greenwich.

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1914

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The new magnetograph house appears to be perfectly satisfactory. The arrangements for maintaining constancy of temperature have so far worked well, the indication of a set of maximum and minimum thermometers showing differences of only a small fraction of a degree Fahrenheit during periods of several weeks between successive visits of the observer to the chamber for the purpose of making scale determinations.

Meteorological Observations.-The mean temperature for the year 1914 was 50.8°, or 1.3° above the average of the 70 years 1841-1910. For the 12 months ended April 30, 1915, the mean temperature was 50.2°. During the 12 months ended April 30, 1915, the highest temperature in the shade (recorded on the open stand in the enclosure of the magnetic pavilion) was 92.1 on July 1. On 21 days the highest temperature in the shade equalled or exceeded 80°. lowest temperature of the air recorded during the same period was 22.3° on January 23. There were 36 days during the winter on which the temperature fell as low as 32.0°.

The

The mean daily horizontal movement of the air in the year ended April 30 was 288 miles, which is 4 miles above the average of the previous 47 years. The greatest recorded daily movement was 791 miles on December 4, and the least 75 miles on April 11. The greatest recorded pressure to the square foot was 26.3 lbs. on December 28, and the greatest velocity in an hour 55 miles on the same day. During the year 1914, Osler's anemometer showed an excess of 11 revolutions of the vane in the positive direction N., E., S., W., excluding the turnings which are evidently accidental.

The number of hours of bright sunshine recorded during the 12 months ended April 30, by the CampbellStokes instrument, was 1573 out of a possible 4457 hours, giving a mean proportion of 0.353, constant sunshine being represented by 1. This is above the average amount, principally on account of a fine June and a fine September.

The rainfall for the year ended April 30 was 24:73 inches, being 0.61 inch greater than the average for the period 1841-1905. The number of rainy days (0.005 inch or over) was 171. September with 0.73 inch was the driest month and December with 6.02 inches the wettest; it was, in fact, the wettest December in the Greenwich series, and the three winter months, with 12.86 inches, the wettest winter in 100 years.

Clocks and Time Service.-The daily time signals

? The values given in last year's report have been increased by 207, arising from a redetermination of the moment of inertia of the deflecting magnet.

The Westminster clock was on two occasions only found to be more than 3.0s. in error.

RADIO-THERAPY: ITS SCIENTIFIC BASIS AND ITS TEACHING.1

THE

HE recent discovery that X-rays and y rays can be defracted into spectra by the natural grating contained in the orderly structure of crystals, sets at rest the question as to the nature of these radiations. They are of the same nature as light-waves, but of very much higher frequency-from 10,000 to 100,000 times as high.

The certitude of the identity of these three classes of radiation leads to issues of much importance to medical science. For medicine had for many years been invoking the aid of the mysterious X and y rays without in the least knowing what these agents were. It now turns out that they are physically identical with light. This fact secure, medical science is made heir to the discoveries of photo-electric science. I shall briefly restate the leading facts of this science

On the living cell y or X-rays produce remarkable effects. The study of these effects in plants dates back several years. Schobert, Errera, Molisch, Guilleminot, and others have contributed to it. The rays may retard cell division, and more especially affect the germinating embryo. They may kill such cells. They may also in very feeble doses promote cell division. Gaskell has specially studied the effects of X-rays on the embryonic cells of the chick. He found that up to a certain amount of exposure the embryo may make complete recovery from the injurious effects of the rays, but that there is a critical dosage beyond which recovery does not occur and development stops. The effects of ultra-violet light in setting up mitosis in certain cells of the eye are beaufully shown in experiments by E. K. Martin (Proc. Roy. Soc., B85, July, 1912, p. 319). Certain ultraviolet rays-the Schumann rays-are said to be always very destructive in their action on living protoplasm, giving rise to cytolysis and death in the cases of spirogyra, amoeba, and other unicellular organisms, in less than one minute. These wave-lengths, which are about half the length of visible rays in the violet, are rapidly absorbed even in air. It has been sug

1 Based on a paper read to the members of the Dublin Clinical Club on March 16, by Prof. J. Joly, F.R.S. Reprinted with abbreviations and some revision from the Scientific Proceedings of the Royal Dublin Society, vol. xiv., No. xxxvii.

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