MUCH interest attaches to an account, by Mr. James Murray, in the January number, of the Zoologist, of a remarkable" encystment undergone by a British species

of so-called water-bear (Macrobiotus). Certain peculiar little yellow elliptical or sausage-shaped packages, from which, when squeezed, water-bears in a quiescent condition spurted out, were, it appears, first observed. Subsequent investigation proved these to be an early stage of the encystment of these creatures. In the species fully examined there is an outer cyst with six rudimentary legs; inside this is an inner, limbless cyst containing at first a fully developed water-bear. Later on the Macrobiotus shrinks to an almost amorphous condition, so that it looks more like a worm. What happens afterwards, and likewise the object of these strange changes, have yet to be ascertained. A similar encystment was detected almost synchronously by Prof. Lauterborn in the case of a Continental species. In the same issue Mr. A. Campbell describes certain naked house-mice similar to a type described in 1856 as Mus musculus nudo plicatus. Since, however, this phase is a pathological development, it has obviously no right to a racial name.

THE U.S. Bureau of Entomology has re-issued (Bulletin No. 26) a report, published in 1895, on the San José or Chinese scale-insect (Aspidiotus perniciosus) in a revised and expanded form, so as to include an account of the investigations and remedial measures which have been undertaken and suggested since that date. The author of the new publication is Mr. C. L. Marlatt, acting chief of the Bureau. The insect, it seems, first made its appearance in America in the early 'seventies at San José, California, on the estate of the late Mr. James Lick, who was in the habit of importing plants from abroad. It was not, however, until 1901, as the result of a special expedition, that its native home was definitely located in north-eastern China. The isolated condition of this habitat is considered to be the reason that prevented the pest from overrunning a large portion of the world centuries ago. Despite the destruction caused to orchards when it once obtains a footing, the pest is now to a great extent under control, mainly owing to a lime-sulphur wash. In some degree the invasion has, indeed, been a blessing in disguise, since the greater care rendered necessary in selection, planting, and culture has largely benefited fruit-growing in general. At one time great hopes were entertained that a Chinese ladybird would form the most efficient restraining agent, but the use of washes and the presence of a parasite were inimical to the beetle.

WE have to acknowledge the receipt of the first three parts of a new,ublication from the Museum für Naturund Heimatkunde zu Magdeburg, edited by Prof. A. Mertens, the director of the museum. By far the most important item in these Abhandlungen und Berichte is a paper by the editor on the urus, or aurochs (Bos primigenius), which occupies the whole of part ii: The author gives a review and digest of the whole of the early literature and documents relating to the ancient wild ox of Europe, as well as of the comments upon them by previous writers. In his opinion, there is no doubt that the name aurochs properly belongs to this animal, although it has often been misapplied to the bison. It is likewise certain that in the time of Herberstain (the middle of the sixteenth century) both aurochs and bison were living in Poland, and that they were seen alive by him. According to other testimony, there was living in the Jaktorowka (or Wiskitki) forest, of the Masovia district of Poland, in the

year 1564, a herd of thirty aurochs. By 1599 the number was reduced to twenty-four, while in 1602 only four remained, these being reduced in 1620 to a single cow, which appears to have been alive seven years later. It seems, however, that a few half-domesticated individuals were living in captivity in 1627. Herberstain's testimony that the aurochs was typically a black (or at all events a very with dark-coloured) animal a light dorsal streak is accepted. Other evidence tends, however, to show that there was a grey variety or phase in Poland, and a red one in central Germany, while the partially domesticated individuals kept in confinement during the early part of the seventeenth century may have developed other colour phases, with partial albinism. Several particulars with regard to the breeding and general habits of the aurochs are also given.

IN a fifth instalment of his "Studies of Mexican and Central American Plants," published as vol. x., part iii.,

In some

of the Contributions from the United States National Herbarium, Dr. J. N. Rose describes a large number of new species. The author being greatly interested in cacti, made them the subject of special investigation during his trip in 1905, and has identified several new and interesting specimens that are described and illustrated. cases numerous individuals cluster together to form a large cushion, as Echinocactus robustus; others develop into strange arboreal structures producing hundreds of nearly erect branches, notably Cereus Webberi, while Echinocactus ingens produces a large circular body that is cut up into sections resembling Dutch cheeses and boiled with sugar to make candy. Even more curious is the liliaceous plant shown in the illustration here reproduced, that is characterised by its thick corky exterior, and lives upon the food absorbed through a few fibrous roots; it forms the type of a new genus, named after Shakespeare's Caliban, Calibanus caespitosus.

IN the Journal of the Royal Microscopical Society for December, 1906, Dr. Alfred C. Stokes contributes a note on a certain form of butterfly scale the structure of which well illustrates certain points in connection with the muchstudied Podura scale. He says:-" These special wing-scales are formed of three distinct membranes, of which the upper and the lower bear longitudinal ribs, between which both membranes are distinctly, even conspicuously perforated by minute apertures arranged in rows more or less horizontal." It appears not to be generally known that the clouded yellow (Colias edusa) possesses pear-shaped wing-scales mixed with the ordinary scales, corresponding more or less closely to Dr. Stokes's description. These special scales seem to take the place of the plumules "of many Pieridae and Satyridæ, and of the battledore scales of Lycænidæ.

66

THE growth of the sudd on the Upper Nile, and the blocking of American rivers with plants of the waterfern, Azolla, are well-known examples of the danger arising out of the undue development of certain water weeds. The most recent instance is recorded from Australia, where the water hyacinth, Pontederia (Eichhornia) crassipes, characterised by its bladder-like swollen petioles and attractive blue flowers, has, owing to its rapid propagation by means of ffsets, become a nuisance in the northern rivers of New South Wales and in Queensland. A report prepared by the order of the Minister for Public Works in New South Wales discusses the origin of the plant, the methods and cost of eradication, and proposes that a Noxious Weeds Bill should be introduced into Parliament.

THE report of the International Committee on Atomic Weights for 1907 is published in the current number (No. 319) of the Proceedings of the Chemical Society. New values are suggested, on the basis of determinations made during the past year, for bismuth, nitrogen, tantalum, and terbium, and the opinion is expressed that alterations are needed in the atomic weights of silver and chlorine. Before, however, recommending any change as regards these elements, the committee deems it advisable to wait for fuller information of the results of determinations known to be in progress, as the new values for silver and chlorine will have an influence on a large number of atomic weights.

IN a paper on the relation of chemical activity to electrolytic conductivity, by Mr. John L. Sammis, published in the Journal of Physical Chemistry (vol. x., No. 8), a large number of experimental observations are cited as disproving the views of Arrhenius and Ostwald that chemical activity in solution is proportional to the electrolytic conduction. The activity of acids in inverting sugar, catalysing esters, and dissolving magnesium is changed by the addition of benzene to the aqucous solution employed at a rate disproportionate to the conductivity. The replacement of one metal by another is said to take place in molten salts or solutions which are the best of insulators as well as in liquids which are good electrolytes. It was found that in sixty-nine non-conducting solutions of copper oleate prepared with different solvents, copper was easily precipitated by lead, whilst in fourteen other non-conducting solutions lead did not replace copper. The general purpose of the paper is to emphasise the view that the solvent is not indifferent to the solute. It is contended that the facts brought forward are explainable only on the hypothesis that " chemical" union occurs between the solvent and the dissolved substance.

OUR ASTRONOMICAL COLUMN. ASTRONOMICAL OCCURRENCES IN FEBRUARY:Feb. 8. 16h. Venus at greatest elongation, 46° 53′ W. 19h. Venus in conjunction with the Moon. Venus 0° 51' N.

12.

9.

Ioh. Minimum of Algol (8 Persei).

6h. 49m. Minimum of Algol (B Persei).

15.

20h. Vesta in conjunction with the Moon.

Vesta

0° 42' S.

19.

6h. 31m. to 9h. 33m. Transit of Jupiter's Sat. III. (Ganymede).

20.

23h. Conjunction of Mercury and Saturn. Mercury 1° 40' N.

6h. Conjunction of Jupiter with the Moon. Jupiter

2° 45' N.

16h. 8m. to 16h. 58m.

(mag. 4'1).

7h. 11m. to 8h. 29m. (variable).

25. 5h. 30m. to 6h. 31m. (mag. 4°2).

26.

Moon occults & Geminorum

Moon occults 5 Cancri

Ioh. 12m. to 13h. 14m. Transit of Jupiter's Sat. III. (Ganymede).

MICROMETER MEASURES DURING THE SOLAR ECLIPSE OF AUGUST, 1905.-At the meeting of the Paris Academy of Sciences held on January 7, M. J. Merlin submitted a paper discussing the micrometer measures made at Roquetas (Spain) by MM. André and Guillaume during the total solar eclipse of August, 1905. From this discussion he arrives at the conclusion that the lunar-parallax constant determined by Prof. Newcomb is not affected by any error sufficiently large to be detected by the measurements carried out. There is, however, room to correct the relative positions of the sun and moon as given in the Connaissance des Temps, although the correction does not modify the apparent trajectory of the moon in regard to the sun; it serves only to advance the position of the former in that trajectory by an amount corresponding to an advance of 11.1 seconds in the calculated times of the contacts (Comptes rendus, January 7).

HEIGHTS OF METEORS OBSERVED IN 1906.-In No. 4152 of the Astronomische Nachrichten Mr. Denning gives the heights, lengths of paths, and velocities of ten large meteors observed in England during 1906. The heights at the commencement of visibility varied from fifty-nine to eightynine miles, whilst those at disappearance varied from twenty-two to fifty-six miles. Seventy-two miles was the length of the longest path recorded, and twenty-four miles that of the shortest. The velocities determined lie between fifteen and thirty miles per second, the latter value having been determined for a Perseid observed on August 5, 1906.

A QUICKLY CHANGING VARIABLE STAR.-In Bulletin No. 9 of the Laws Observatory, University of Missouri, Mr. F. H. Seares discusses the observations of the quickly changing variable star R.R. Draconis (188.1904) which were made at that observatory during 1905-6. The variable is of the Algol type, with a period of about 2.8 days, and its light-curve is peculiar in being extraordinarily steep about the time of minimum. The latter could not be determined exactly, because the star becomes invisible for about two hours in the 7-inch refractor employed, but the observations plainly showed that the range is greater than three magnitudes, and that the rate of change at the time of disappearance is one magnitude in half an hour. The normal magnitude of this object is 9.98, and the elements of its period, as determined from these observations, are:

Min. J.D. 2417026-682 +2.831079d. E. G.M.T. Some of the residuals suggest the possibility of a variation in the period, but for the present this possibility remains very uncertain.

THE ERUPTION OF MATAVANU IN
SAVAII, 1905-6.

THE last-issued number of the Zeitschrift der gesellschaft für Erdkunde zu Berlin contains an account of a very remarkable volcanic eruption which had been in progress for more than twelve months in September last in the island of Savaii. The volcanoes of this island had been quiet. for more than a century when, in 1902, two minor outbreaks occurred, and in 1905 a greater eruption commenced, causing so much anxiety and alarm that the German Colonial Administration sent to Prof. K. Sapper, of Tübingen, a collection of specimens, photographs, and newspaper and other reports, from which he has compiled an account which is interesting in spite of its inevitable incompleteness.

The eruption was ushered in by a series of earthquakes lasting from July 25 to August 1, 1905; at half past nine on the night of the last-mentioned date a loud detonation

could be obtained, so Dr. Grevel and his party worked round by the east, where the surface was covered with countless bodies of moths, attracted by the glow of the crater and killed by the vapours rising from cracks in the surface of the lava flow; the same vapours had proved fatal to a flying-fox, a dove, and a sea-gull. From the southern edge a good view of the crater was obtained; it was about 300 metres in diameter, filled with a lake of molten lava in gentle ebullition, caused by the rise of steam bubbles, and from the centre a gentle streaming to the north commenced, which increased in rapidity until the lava disappeared in a cataract into a cloud of steam, and presumably joined the stream over the surface of which the party had ascended.

On reaching the sea, the lava flowed out to the reef, where its end, being cooled by the surf, formed a wall between which and the coast the lava flowed quietly along the lagoon. At its end the sea was in violent ebullition, dense clouds of steam were formed, and for

100 metres from the end of the flow the sea was boiling hot, and fishes, killed and cooked by this boiling sea-water, were collected and eaten by the natives. In a few places the lava flowed over the reef into the deep water outside, and where this occurred its progress was marked by violent geyser-like explosions, which were mistaken by some people for fresh volcanic eruptions, but were in reality due to steam formed under the still liquid lava. We reproduce a very striking photograph of one of these geyser-like explosions at the front of a lava stream flowing into the deep The lava was remarkable for its fluidity, and issued in great quantity; according to a map attached to Prof. Sapper's paper, the area covered by the lava extends about 6 kilometres to the west and 12 kilometres to the north-east of the volcano, and has a width of from 2 kilometres to 5 kilometres ; it has filled the lagoon for about 8 kilometres along the coast, destroying several villages and rendering others uninhabitable by cutting off their water supply, while several small promontories of lava were thrust forward beyond the reef.

was heard, and shortly after pillars of fire " were seen issuing from a valley known as Matavanu, some 12 kilometres from the coast on the north-eastern side of the island. At first the eruption was of an explosive character, and does not seem to have been very violent, as the estimates of the height to which matter was thrown do not exceed 200 metres, and the hill formed was never more than 150 metres in height. On August 9 lava began to flow, at first in small quantities, afterwards more abundantly, until it reached the coast on December 6, and flowed down to the sea at intervals up to the end of September, 1906, the date of the latest reports received by Prof. Sapper. During this period the outflow of lava seems to have been continuous, though varying in amount, and unaccompanied by any considerable degree of explosive activity.

Many people visited the volcano during the eruption, and an interesting account by Dr. Grevel is reprinted from the local newspaper; his party made the ascent on April 23 last, over the crust of the lava stream, which was smooth and easily traversed, and cool enough for the Samoans who accompanied him to walk over it. The solid surface of the lava stream was broken at intervals by vent holes, the one nearest the crater being at first mistaken for a parasitic cone, as the crust of the lava rose in a gentle convexity to the orifice, which was much smaller in diameter than the cavity underneath. Thick, sulphurous vapours prevented any sight into the cavity, and large stones thrown in gave no clue to its depth, as their fall was unheard. Four of these vent holes were examined, which repeated the features of the first on a smaller scale, and the party then climbed to the crater by an easy ascent over the lava flow on the northern side. Owing to the drift of the south-east trade wind, no view of the crater

sea.

RESEARCH IN TROPICAL MEDICINE AND HYGIENE.

(1) TH

HE greater part of the first report is occupied with an elaborate memoir by Drs. Thomas and Breinl on trypanosomes, trypanosomiasis, and sleeping sickness. It comprises a description of cases of sleeping sickness, a full account of inoculation experiments with the Trypanosoma gambiense, from which the conclusion is formulated that the trypanosomes of sleeping sickness of Uganda and of the Congo Free State and of trypanosomiasis are identical, together with an account of the, pathological anatomy and histology of trypanosomiasis, the action of various drugs on trypanosomes, and experiments with the trypanosomes of surra, mal de caderas, dourine, &c.

The late Mr. Dutton and Dr. Todd contribute an important memoir on human tick fever in the Congo Free State, with an appendix by Mr. Newstead on the anatomy of the tick (Ornithodoros moubata) which conveys the disease.

1 (1) "The Thompson-Yates and Johnston Laboratories Report." Edited by Rubert Boyce and Charles Sherrington, with H. E. Annett, Benjamin Moore, Ronald Ross and E. W. Hope. Pp. 141. Vol. vi. (New Series), Part ii., December, 1905.

(2) Ibid. Vol. vii., Part i., February, 1906. Pp. 88+plates.

(3) "Rapport sur l'Expédition au Congo, 1903-5.' Par J. Evere't Dutton and John L. Todd. (École de Médicine Tropicale de Liverpool, Mém. xx.) Pp. 75. (All published for the University Press of Liverpool, by Williams and Norgate, London, 1956.) Price 55.

(4) "Second Report of the Wellcome Research Laboratories at the Gordon Memorial College, Khartoum." By Andrew Balfour.

Lastly, Surgeon Ross, R.N., contributes a short paper on the habits of the marine mosquito (Acartomyia zammitii).

(2) The second report contains papers on a new species of louse (Haematopinus stephensi) which acts as the intermediary host of a new hæmogregarine parasite in the blood of the Indian field rat, by Mr. Christophers and Mr. Newstead; a note on the anatomy of Gastrodiscus hominis, a human fluke, by Dr. Stephens; a revision of the Sarcopsyllidæ, by Dr. Karl Jordan and the Hon. N. C. Rothschild, a family of fleas which includes the jigger, and the rat flea supposed to transmit plague to man; and a description of the maiotic process in Mammalia, by Messrs. Moore and Walker. The last-named paper is illustrated with a number of beautiful plates, and is well worthy of study.

(3) In this report the late Mr. Dutton and Dr. Todd, after some general remarks on the conditions favouring the spread of malaria, describe the conditions existing at some of the towns and posts of the Congo Free State, and formulate recommendations for remedying these. Dr. Breinl and Mr. Kinghorn describe experiments showing that the Spirochata of African tick fever is infective for the horse, dog, rabbit, guinea-pig, rat, and mouse in addition to monkeys, whereas the Spirochaeta obermeieri of relapsing fever is infective for monkeys only. Dr. Breinl has also compared the immunity produced by these two Spirochetes, and finds that each strain produces considerable active immunity against re-infection, but does not produce immunity against infection with the other strain. The course of the disease also varies with the two strains, and the conclusion, therefore, is that tick fever and relapsing fever are produced by different species of Spirochetes.

(4) The second report of the Wellcome Research Laboratories of the Gordon College, Khartoum, by Dr. Andrew Balfour, the director, maintains the high standard of the first one (see NATURE, vol. lxxi., p. 605), both as regards the nature of the work recorded and the manner in which it is presented to the reader. Nearly half the volume comprises records of mosquito work in Khartoum, of biting and noxious insects, mosquitoes, and other human, animal, and vegetable pests of the Sudan. Dr. Balfour describes a hæmogregarine parasite of the jerboa and a leucocytozoon of mammals, and contributes a report on cattle and equine trypanosomiasis in the Anglo-Egyptian Sudan. Fortunately, human trypanosomiasis and sleeping sickness do not yet seem to be endemic in this part of Africa, nor has the tsetse-fly which conveys it (G. palpalis) been described here. In the chemical laboratory a considerable amount of work has been done by Dr. W. Beam, the chemist, on water analysis, Sudan grains and gums, &c. The travelling naturalist, Mr. Sheffield Neave, records many interesting observations on blood, blood parasites, &c., of birds, fish, and other animals.

A GENERAL article upon the proceedings of the

American Association for the Advancement of Science at the meeting held at New York during the Christmas vacation appeared in NATURE of January 24 (p. 304). Through the kindness of the general secretary of the association, Dr. L. O. Howard, we have received copies of several of the addresses delivered by the president and by the chairmen of sections, but limitations of space will not permit us to publish any of them in full. The subjoined extracts from these addresses will, however, afford an indication of the subjects considered and the views expressed.

EDUCATIONAL THEORIES, ANCIENT AND MODERN.'

The Greek idea of education and culture was based apon the existence of a privileged class, fed, clothed, and sheltered by the labour of slaves-a real aristocracy devoted 1 From an address delivered by Prof. C. M. Woodward, president of the American Association.

to war, art, literature, and luxurious living. The sway of the so-called classic idea of education has been, and still is, one of the marvels of history. The splendour of Greek art, the brilliancy of Greek literature, and the keenness of Greek logic, have held the world as in a trance, unable to break away from its charms-though it has been unsuited to other peoples and other social conditions. Francis Bacon more than any other man showed the inadequacy of the classic method, fine as it was along certain lines, and the comparative worthlessness of scholasticism, and he opened the eyes of the educated people of his time to the wealth of opportunity for interesting and profitable study in the great laboratory of nature, and, better than all else, he set forth the dignity and intellectual value of science study, and vigorously scouted the idea that the usefulness of scientific truth in any degree detracted from its educational value.

But none of the writers touching on education, with the possible exception of Froebel and Pestalozzi, not even Locke, Milton, or Dr. Samuel Johnson, looked at the matter from the scientific standpoint, which takes into account, first, the physiological laws which govern the growth and development of the brain; secondly, the exterior stimuli for promoting that growth most successfully; and, thirdly, the kind and quantity of knowledge and skill one must have in order to meet most completely the demands of a carefully selected occupation.

Every good teacher aims to make his subject as interesting as possible to his pupils. If they fail to take a lively interest in it, something is wrong; either it is not properly presented, or it is over their heads, or it is clearly of no earthly use. Natural lack of capacity on the part of the child is rarely a valid reason for failure if the child be healthy and normal. I have learned to discredit the truth of the oft-told tale that "John has no capacity for " such a subject-mathematics, for example. He never could learn mathematics-he takes no interest in algebra, and he hates geometry, &c. Our higher schools and colleges are full of young people who protest vigorously that they never could, and never can, understand or take any pleasure in or gain any profit from certain studies. I firmly believe that every normal person, at least nine out of ten of the children and youth at school and college, can fairly master and actually enjoy and profit by, not only mathematics, but by every subject in the curriculum if it be properly taught, and under proper conditions as to age and preparation.

Attention is as necessary to the growth and development of the brain as exercise is to the development of a muscle, and interest is the condition of a lively attention. When in a school or lecture-room the limit of close attention is reached, the lesson or lecture should close, for the educational process has already stopped. It is not only useless, but it is worse than useless, to go on when the class or audience refuses for any reason to attend. I therefore doubt the educational value of subjects which are not, and perhaps cannot be, made interesting.

Of course I do not claim that all selected studies can be made equally interesting, or that any one study can be made equally interesting to all pupils, even when the pupils are properly graded, but I do claim that a lively interest is necessary, and that educational progress is very nearly proportional to the strength of that interest.

Perhaps the most valuable contribution to the science of education has come through a study of the laws which obtain in the growth and development of the brain, and the conditions under which that growth and development is most healthy and complete. There are times and seasons for the development of the mental and moral faculties as there are of the physical faculties. While such times and seasons are not precisely the same for all children, we find that all attempts at premature development are not only worthless, but are permanently injurious. Precocity is now regarded as a species of brain deformity. Plants and animals may be forced, and unusual and interesting results may be produced by forcing, but no one of us wishes a son or a daughter to be a prodigy in one direction at the cost of normal development in other directions.

The psychologists tell us that the brain cells develop as do other physical organs, not only through thought,

but through muscular activity and the exercise of our senses. Accordingly, a healthy and timely growth and development of the brain is to be promoted by an education involving a great variety of activities, skilfully adjusted as to quality and quantity to the mental and physical status of the child.

Closely related with this of brain culture is the subject of manual training, which has recently gained a foothold in our scheme of rational education. Its nature and educational value are still under discussion.

The manual-training movement stands inevitably as a criticism upon the system of education which came down the ages through the fathers to us, and naturally the latter stands on the defensive. It also is a standing reproof to the old wasteful, unscientific method of teaching apprentices the theory and uses of tools. It is for educational science to justify the ways of progress, which lays aside the idols of the past and erects new temples and opens new kingdoms. Of all the temples, none is finer, none is more glorious, and none should be more scientifically planned and reared than education.

The evolution of the fully fledged technical school, or the technical department of the university, has taken place during the last half-century, and yet its broad, stimulating, attractive features have a following which bids fair to double the attendance of college and university students. This does not mean that letters and polite learning are being neglected, but that a new constituency is eager for the new education. This new education, though it recognises at all points a high order of usefulness, and contains little that is conventional, is only remotely professional. If ever its curriculum becomes narrow, it is quickly condemned by the best representatives of an education which combines utility with culture. No longer can the "Levites of culture, as Huxley calls them, claim to monopolise. liberal education. The new education can be as liberal as the old, and both can be narrow. Fortunately, they flourish side by side, and the future shall choose the excellences of each. An adequate science of twentieth-century education will evaluate the characteristics of each, and bring the wisdom of the past, not its foolishness, to nourish the wisdom of the future.

ACCURACY OF ASTRONOMICAL CLOCKS.1 The accuracy with which our astronomical clocks perform their function is subject of a interest. The earliest star catalogue of precision is that of Bradley. In discussing the performance of his clock, I have used the adopted rates as given by Auwers in his re-reduction of Bradley. The monthly means of the rates from July, 1758, to July, 1759, were taken, and the difference of each rate from its monthly mean. Then the mean of these differences, without regard to sign, was taken for each month.

The rates of two other clocks of the Greenwich Observatory were likewise discussed, the standard clock for the year 1850 and that for 1900, the adopted daily rates as published in the annual volumes being used. The first of these was kept in the observing room, and thereby subjected to large variations of temperature, while the second, made in 1871 by E. Dent and Co., was fixed to the north wall of the magnetic basement, as in this apartment the temperature is kept nearly uniform. The pendulum of this latter clock is provided with barometric as well as thermometric compensation.

There are two well-known clocks which should be mentioned, and in conclusion I will give some hitherto unpublished data concerning the clock with which I have been working during the past three years.

Probably no clock has had its rate more thoroughly discussed than Hohwü No. 17, the standard clock of the observatory at Leyden. It was set up in the transit room in 1861, and in December, 1898, was removed to the large hall of the observatory, where, enclosed in two wooden cases, it was placed in a niche cut in the pier of the 10-inch refractor. Further, to guard against sudden changes of temperature, the niche is closed by a glass door. At the meeting of the Royal Academy of Sciences at Amsterdam, held September 27, 1902, Dr. E. F. van de Sande Bakhuyzen submitted a formula as the best repre1 From an address delivered by Prof. W. S. Eichelberger chairman of the Section of Mathematics and Astronomy.

sentation of the daily rate of the clock, and gave the result of a comparison of the observed daily rates 1899-1902, the average interval of time for each rate being six days, with those computed by means of the formula. I find that during the year 1900 the mean of these differences is 0.028s., and the largest difference is 0.071s.

About 1867, F. Tiede installed at the Berlin Observatory a weight-driven clock enclosed in an air-tight case. The original escapement was replaced in 1876 by a gravity escapement, and the clock continued to give satisfaction certainly up to 1902, when it was dismounted for cleaning. The only published rates that I have been able to secure are those during twelve weeks in 1877-8. During this period the average deviation of the observed daily rates, the average interval for each rate being six days, from the mean daily rate for the entire period is 0.030s.

In 1903 there was installed at the U.S. Naval Observatory one of Riefler's clocks, No. 70, with a nickel-steel pendulum, the impulse being communicated to the pendulum through the suspension spring. This clock was enclosed in an air-tight glass case, and was mounted in a vault where the temperature was artificially controlled. The definitive rates have been determined from September, 1903, to May, 1904, but, unfortunately, during this entire period we were unable to prevent the glass case leaking, and there was a variation of temperature in the vault of about 5° C.

Collecting together the results obtained, we have :-
Mean Deviation of Daily Clock Rate.
Clock

Date

Mean Deviation

...

1900

0'028

1904

0'015

Leyden Observatory
U.S. Naval Observatory

FACT AND THEORY IN SPECTROSCOPY.1

Any treatment of the production of radiation falls more or less naturally into three parts, namely :-(1) the radiation of solid and liquid bodies which is almost, but not quite, independent of atomic structure; (2) the radiation which takes its rise in radio-active substances, and which is apparently dependent upon atomic collapse; and (3) the radiation of gaseous substances, dependent almost entirely upon normal atomic structure, and possibly also upon the mode of excitation.

The subject to which consideration is now invited has Radiation to deal only with radiation of this third class. which in terms of the electron theory is said to be due, not to abrupt or discontinuous acceleration, but to periodic acceleration.

Briefly defined, spectroscopy is that science which has for its object the general description of radiation, including the production of radiation, the analysis of radiation, the registration of radiation, and the measurement of radiation.

The theory of separating, recording, and comparing radiation is by no means simple or complete. That these last three operations demand in practice the highest degree of skill is exemplified by the work of Rayleigh, Rowland, Michelson, Perot and Fabry, and Hale.

There is, however, a certain very true sense in which these last three processes are merely preparatory to a more profound study of the first, namely, the production of radiation. From this point of view, spectroscopy hinges upon the radiant atom-if there be an atom-and may be defined, imperfectly and narrowly perhaps, as the science of the radiant atom.

More than one brilliant and partially successful attempt has been made within the last quarter-century to establish an adequate foundation for this science by devising what may be called a satisfactory atom. But before considering any of these attempts, it may be well to state briefly what seems to be the criteria by which any such foundation is to be judged.

Perhaps it may be fair to consider that atom as most competent which will explain satisfactorily the largest number of the following nine facts :

1 From an address delivered by Prof. H. Crew, chairman of the Section of Physics.