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THE author states that his object has been to supply the long-felt want of a power of recovering a given colour sensation and of a colour nomenclature by which that sensation may be quantitatively described. To this end scales of red, vellow and blue were constructed of glass slips, the slips of each scale being all of one colour with a regular variation in intensity from 0.01 to 20 units, equal units of the three scales being in colour equivalence with each other.

The test of equivalence is that a white light viewed through equal units of the three scales should give no evidence of colour. . . . The fogs on Salisbury Plain furnished the light actually used." It was found that red, yellow, and blue were the only colours suitable for systematic work, and that any The colour could be produced by their combination. dimensions of the unit are, it is said, necessarily arbitrary, but the scale-divisions are equal, while the unit itself is recoverable.

The colour to be tested is matched by that of the light transmitted by one of the glasses, or by several superposed, equality of luminosity being secured, when necessary, by the interposition of a neutraltinted combination between the eye and the coloured object. A specification of the glasses employed is registered, according to certain rules, as a formula which defines in terms of the author's constants the colour “developed," and supplies data for its future reproduction.

To those who are accustomed to regard the spectrum as the natural basis of colour experiment the author's method cannot but appear crude and unscientific; but, given a sufficient supply of carefully selected glasses, it is probable that much useful work might be done in a rough and ready way by its means. An example occurs in the quantitative study of the colour of the human blood in health and in disease, which is illustrated in plate vi.

The book concludes with an exposition of Mr. Lovibond's new theory of colour.

Index Phytochemicus. By Drs. J. C. Ritsema and J. Sack. With introduction by Dr. M. Greshoff. Pp. 86. (Amsterdam: J. H. de Bussy.) DR. GRESHOFF explains in the introduction to this volume that it originated in a card index to the literature of plant chemistry compiled for use in the laboratory of the Colonial Museum at Haarlem, where the work carried on consists principally of the investigation of the proximate constituents of plants.

The index enumerates the names of more than two thousand plant constituents, and gives in each case the percentage composition, formula, melting or boiling point, and at least one reference to the literature - usually Beilstein's "Handbuch," though in a few cases the references are to original papers. volume also contains a short but useful bibliography of plant chemistry.

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The information given in the tables, so far as can be judged from trials in a few cases, appears to be accurate, and the index should prove useful to chemists engaged in the investigation of plant products.

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.]

Eclipse Predictions.

Ir is always interesting to compare the results of observation with those predicted by calculation. In the case of the recent total eclipse of the sun this is rendered difficult by the want of agreement in the predictions of the two most used authorities, the Nautical Almanac and the Connaissance des Temps. The discrepancies in the predicted duration of totality and of the breadth of the band traced on the earth's surface by the total phase are made apparent in the following table. It is compiled from the table in the Nautical Almanac headed "Limits of total phase of the Solar Eclipse, " and the corresponding table "Limites de in the Connaissance des Temps entitled l'Eclipse totale et Durée de la Phase totale sur la Ligne centrale.' Entries for as nearly as possible the same time in each table have been taken and are placed together :Column A contains the authority, Nautical Almanac (N.A.) or Connaissance des Temps (C.T.).

Column B contains the time (G.M.T.) for which each prediction is made.

Column C contains the calculated distance (in nautical miles) and the bearing of the northern limit of totality from the corresponding southern limit.

Column D contains the durations of totality on the central line as predicted by the one authority and (in brackets) as interpolated from the prediction of the other. Column E contains the differences of these pairs of values.

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It will be seen that, for stations in Spain and the adjacent Mediterranean, the duration of totality on the central line was predicted by the French authority to be from seven to eight seconds longer than by the British authority. In the same region, the width of the band of totality is from ten to eleven nautical miles greater by the French than by the British prediction. The orientation of the line connecting the two limits of totality also differs considerably in the two tables.

It is reported that at Sousse and Gabes, two towns in Tunisia, the eclipse was partial, while a total eclipse had been predicted for them. The prediction for these places would surely rest on French authority: we are therefore entitled to conclude that the mistake has been made by the French calculators. An excessive estimate of the width of the band of totality would almost certainly be accompanied by an excessive estimate of the duration of totality, and the table shows that both estimates are considerably greater in the Connaissance des Temps than in the Nautical Almanac. J. Y. BUCHANAN,

October 13.

Absence of Vibration in a Turbine Steamship. RETURNING homeward to Paris the middle of September from the Tripoli eclipse, and finding passage to America difficult to obtain, I chanced to learn that the triple-screw turbine steamer R.M.S. Virginian was sailing from Liverpool for Montreal on September 30, so I was very glad to have the opportunity of a voyage in a ship full powered with this novel type of propulsion. After a week on board I have no hesitation in saying that for freedom from

the nerve-annoying tremors incident to the usual reciprocating engines, the Virginian has proved far and away the quietest steamship I have ever voyaged on. Excellent evidence of this, I think, lies in the exceptionally large number of passengers who dined comfortably in the saloon at the roughest period of our entire passage. There was a fairly heavy sea on, and the ship was by no means free from wave-origined motion. So I am quite of the opinion that sea-sickness and all its train of discomforts must be greatly aggravated by the engine-borne tremors of the ordinary steamship, and that many people who are delicate sailors under ordinary conditions might take ocean journeys with comparative comfort in a turbined ship.

So unostentatious are the rotary engines of the Virginian, let alone their occupying but one-fourth the space of the usual expansion engines, that the quietness of their powerful and effective working, in every part of the ship, was continually deceiving one into thinking that the vessel had lost headway, or might have come to anchor altogether. Especially was this true in the dining saloon, that most critical of all spots, where one could rarely detect so much as a ripple on water in a glass, although going ahead at full speed of 15 knots.

To my mind the Virginian seemed to behave all the voyage quite as if her motive power were entirely without her; in fact, she could scarcely have ridden more smoothly, or with less of that exasperating vibration (the unceasing action of which, I am convinced, is a prominent factor in inducing mal de mer), if she had been towed at the identical speed by a huge hawser. DAVID TODD. R.M.S. Virginian, Straits of Belle Isle, October 4.

A Parasite of the House-fly.

REVERTING to the recent correspondence under this heading between Mr. Davenport Hill and Prof. Hickson (NATURE, August 24 and 31), I recall that a few years back many house-flies with Chelifers attached were sent to me at the Natural History Museum for determination of the species and explanation of the phenomenon. The first task was as easy as the second was difficult. The Chelifer was in most, nay in all, cases, so far as my memory serves, Chernes nodosus. But those who suggest that the explanation is to be sought and found in the value of the habit as a means of securing dispersal hardly realise, I think, the difficulties in the way of its acceptance. Chelifers are minute, active, and, for arthropods, not exceptionally prolific. Hence the sufficiency of "elbow-room "for the survivors of a family of, say, forty, on the site chosen by the female for her progeny does not coincide with the view that they have special need of transportation. Moreover, when we remember that a Chelifer attached to a fly is exposed to the danger of being killed by the enemies of that insect, and also to the great chance of being landed in a wholly unsuitable environment, it can hardly be maintained that the advantage derived from this method of dispersal has been a sufficiently important factor in survival to preserve and foster an initial instinct to grab and hang on to the legs of flies. That the aerial porterage thus secured, whether fortuitously or intentionally," must be a means of dispersal is too obvious to dispute; but I do not think more than that can be claimed for it, since it is as likely to end in failure as in success.

Chelifers may be found not uncommonly beneath the wing-cases of large beetles. Presumably this habitat has been adopted for the sake of the food supplied by the parasitic mites infesting the beetles. This fact, I think, suggests a line of investigation which may lead to a more satisfactory explanation of the association between Chelifers and flies than that put forward in Prof. Hickson's letter. Zoological Gardens, October 14. R. I. PocoCK.

Incandescence of Meteors.

It is with great diffidence that I approach this difficult subject, but the theory that the incandescence of meteors is due to the heat generated by the friction between these bodies and the molecules of gas composing our atmosphere

I have always found difficult to believe. The following theory is one which has occurred to me, and seems quite a plausible one. Meteors are usually of a metalliferes nature, and consequently will have a comparatively electrical resistance. When they approach the earth the. will enter a magnetic field, and they will cut the lines ed force of this field at a high velocity. A high electrice potential will be generated, and consequently electr currents which will be inversely proportional to the reset. ance. The electrical energy thus produced will be diss pated in heat, and if of sufficient intensity will raise the meteor to incandescence. The truth or otherwise of thes theory could, I believe, be calculated, as the data necessary for doing so will be at the disposal of readers of NATUMF who make this branch of astronomy their study. Th theory may have already been advanced, as I am rot in touch with the latest developments of the science. Coatbridge, September 5. GEORGE A. Bros.

THE electric currents which the author of the above lette

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regards as possibly constituting an efficient source of the luminosity of meteors must no doubt arise, and play certain part in the heat and light development. But tr measure in which they can be supposed to contribute to it must clearly be extremely small; or rather, it must be incomparably subordinate to the intense ignition of the produced, not at all by friction,' but by the air's adiabat. compression against the front surface of the meteorite which is certainly quite competent, by itself alone, to devel what may be said to approach pretty nearly to fabulous degrees of temperature. If the kinetic energy of translation, in foot-pounds (v2 2g), of 1 lb. of the air propelled fat, só, 30 miles per second) with the meteor's speed (v feet se.) on its front face, be divided by 330, the number thus obtained (1,180,620° C., in the case supposed) will be the number of centigrade degrees through which it will to heated by the pure process of compression, supposing that the air can continue to subsist at all with its ordinary mechanical deportment and thermodynamical properties affected at that enormously high temperature. In the further forward, gradually advancing layers, and in th laterally escaping currents of the air, on which the high forward speed of the meteor is only partially impressed, and which move more slowly on their various courses, pa compressions are correspondingly less, and the lower but still exceedingly high temperatures can be similarly cales:lated from any fair estimates of the air's collective or absolute velocity of translation in those different positions

It is in the different rates of transport of these heated air-streams, all of them, as well as the highly attenuat. motionless atmosphere around, affording very easy passag ways to electricity, across the earth's magnetic field or system of lines of magnetic force, that fitting circuits can certainly be found (either passing through, or else entir omitting the meteorite itself), in which, in the suggested in the above letter, electric currents may be quiccertainly concluded to be magneto-electrically induced For while one part of a closed air-circuit resting against the meteorite's front surface, and another part of it situatel in the still atmosphere in front of or behind it, would tjourneying towards or from each other with full meteorspeed, the circuits so composed would be most suitab's conditioned for developing induced currents round them in 1 Although a very general belief, it is as yet an entirely mistaken supposit that the high speed of impact of a meteorite into the rarer regions of th= atmosphere reduces the air, by giving it no time to dissipate itself in front of the meteorite, to a state of granulation, or to a wedged throng of molex c producing heat by friction inter se and against the surface of the meteant Just the reverse of this condition is, however, really true, that the remains a perfectly and frictionlessly elastic fluid, however much it is n pressed and intensely heated by the impact. The speeds of sound-waves in the heated air which perform the office of transmitting and maintaining the orderly array of pressures in the streaming flows, at length differ in defect in fact, from the air's speeds themselves in proportions which, as is * mount up to meteor-speeds of many miles per second, only decline a totically to about the ratio 1:5, or nearly 1:2). Since, thes, these sound-waves, which convey the strokes and shocks of the collision to a fro between the meteor-centre and the surrounding air, arise and tr... Voi in the moving field of the compressed air as if it were at rest, it is easy perceive that by their extremely rapid actions a most exceptionally perfe elastic fluid relation, or steady disposition of the lines, or lanes of air-Blow and blast-pressure, must really be established and maintained in vENÍ persistent shapes and contour, in the swirl of incandescent air which f

the meteor's head.

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their quickly altering enclosures of a constantly changing number of the earth's lines of magnetic force, while thus

rapidly opening out or closing up. But the very short

extent, not probably much exceeding some few feet or yards, which the swiftest moving part of such a circuit, in meteornuclei of various sizes, would embrace, and again the oftproved weakness of the earth's magnetic field for exciting such induced electric currents, scarcely allow us to expect that any very high voltages would be attained in even the most select cases and the most favourable choices of conditions of such meteoritically produced air-circuits. The hottest, and therefore also probably the best conducting portion of each current's path, compressed against the meteorite's front surface, would also not, presumably, be that in which the heat and light producing action of the Current would be strongest, since this would rather be used up in producing brush and glow discharges through the more resisting portion of the circuit in the outer air. The interior parts themselves of stony meteorites, when they Fave fallen, have not been found, by either sight or touch,

Turnish any proofs of having been much heated, but ir tense effects of heat and fusion on the outer surfaces of fallen meteorites are always very obvious.

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While nothing seems to point to any very easily discernible actions of electric currents immediately around a meteor's head, unless we may ascribe to electric agency the occasional production of an of sparks, or of a misty envelope of light enshrouding it, the stream of heated dust and vapours which travel in a meteor's wake, extending to considerable widths and lengths, as may be often noted, is perhaps a more visibly displayed, and a more evidently and distinctly active scene of luminous discharges of induced electric currents: for the accumulated flow behind the meteor-head resembles in some degree a columnar, vaporous follower of the metecrite itself, left to pursue its course along the meteor-track when the, nucleus has disappeared. Being thus virtually a shooting-star of a long-extended shape, but of too dwarfed velocity to raise itself by heat to incandescence, the same induced electric Currents as were above inferred to be developed in the meteor's head would here continue to evince themselves along the column by glow discharges in the vapours and the outer air, so long as sufficiently swift flow of the vapours can be persistently maintained through the retarding resistances of the opposing atmosphere. Thus, a fairly intelligible raison d'être by electric current interventions may not impossibly have been incidentally divulged, by means of the recourse proposed by Mr. Brown to magnetoelectric actions, of the long-enduring light-streaks left along the paths of all the swifter class of shooting-stars and larger meteors; the real modus operandi of those streaks having always presented to meteor observers a mysterious question for discussion, never admitting hitherto of satisfactory solution by known experimental illustrations, or of any quite surely sound elucidation by less trustworthy conjectures. A. S. H.

A R re Game Bird.

I THINK it is worth recording that on Thursday, October 5, Sub-Lieut. H. R. Sawbridge, R.N., shot a quail, Perdix coturnix, on Lopham Fen, close to the rising of the waters, the common source of the Waveney and the Ouse, near Diss, Norfolk.

The bird, either a hen or a young male, was very fata beautiful little specimen.

The last quail known (by me) to have been shot in this neighbourhood was in the fifties of the last century, by Mr. Henry Button, of this parish.

I understand that this bird was much more frequently found in the middle of last century in the neighbourhood of Great Yarmouth, and that, as a rule, it was found singly, as this was, in the autumn.

It is being preserved by Mr. Cole, of Norwich. What was a little foreign bird like this doing singly and alone on our eastern counties' heaths and fens?

Is it a case of lost or strayed, or what is it?

It would be interesting to know whether other specimens of the quail have been heard of inland in the eastern Counties of late years. JOHN S. SAWBRIDGE. Thelne tham Rectory, Diss, Norfolk, October 16.

PHYSICAL LABORATORIES IN GERMANY. THE Director-General of Education in India has just published a valuable work in a report by Prof. Küchler, of the Presidency College, Calcutta, on physical laboratories in Germany. It forms one of a number to be included in a volume of the series of occasional reports.

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Prof. Küchler was placed on special duty to inquire into (1) the methods adopted at the universities and polytechnics of Berlin, Munich, Vienna, and other prominent universities and technical institutions in Germany with regard both to the ordinary study of physical science and to the character of the investigations and the system pursued in the case of students who are entering upon a course of independent research. (2) The construction and equipment of modern German laboratories, the special merits of scientific instruments of German manufacture, and the facilities for standardising these instruments which are offered at central institutions in Germany."

In the course of his tour, lasting more than six weeks, the principal universities and technical schools were visited, and the report sums up the information in a useful manner. It is naturally divided into two sections corresponding to the two parts of the reference; the first deals with the methods of study, the second treats of the construction, methods of equipment, &c., of the laboratories. The training of the university undergraduate of necessity differs from that of the pupil of the high school, and both methods are described at some length. Attention is directed to the importance of the set lecture in the scheme of education; the number of lectures given during the session in a university such as Berlin is very considerable, and each lecturer has the use of a properly equipped lecture-room and apparatus. The importance of the organised teaching of practical physics, for medical students, chemists, and engineers, in addition to the professed physicist, is now realised in Germany, and in an appendix, which, however, is not printed in the report, details of the practical instruction at some of the universities and technical colleges are given. In view of the large number of students in some of the German universities, the numbers attending practical classes, as given on p. 7, seem small. At Berlin there are 140 students in two divisions, each under three assistants. The average number of students in the charge of a single assistant comes to twenty-two or twenty-three, which is probably about the same as in one of our well organised English courses.

Prof.

Students who propose to take a degree in physics work usually for two years at a dissertation. Küchler specially directs attention to the fact "that students are discouraged from commencing the final stages of their labours before they have been thoroughly trained in practical manipulation and have carefully gone through a complete course of laboratory work such as is represented, say, by Kohlrausch's very elaborate handbook." This fact is sometimes conveniently forgotten by those who urge the adoption of the introduction of research work at an earlier stage in our English training; the average number of these research students is said to be five or six, though, of course, at Berlin, as indeed at Cambridge, the number is much larger. To illustrate the construction and equipment of the laboratories, Prof. Küchler has given in full the plans of a number of representative institutions, and these plans form a most valuable part of the report. They will enable a professor building or organising a

1 A Report to the Director-General of Education in Irdia by Prof. G W. Kuchler.

laboratory in India to see readily the arrangements which have commended themselves in Germany, and the report directs attention to the modifications which will be needed to adapt them to Indian conditions.

Perhaps the details which strike an English student most are the number and size of the lecturerooms, the accommodation provided for the museum, and the absence of rooms specially designed for elementary classes of large numbers.

The Director-General deserves the gratitude of all interested in the organisation of the teaching of physics for having initiated this work, and Prof. Küchler is to be congratulated on the manner he has carried out his task. Still, a companion volume is needed. British physical laboratories of to-day have many admirable points. A book that described

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THE ESSEX FIELD CLUB.

order to mark the completion of a quarter of a century's scientific work in the county of Essex, the above society has published the first issue of Yearbook and Calendar " which will be found of interest to all who follow the work of our local scientific societies. This extremely active association was founded in 1880 by Mr. William Cole, the first president being Prof. Meldola. The work of the club has been noticed from time to time in our columns, and the present "Yearbook " contains, as an appro priate opening chapter, a history of the society by Mr. Miller Christy, who is now president. That the club has carried out the objects for which it was founded, and that it has more than justified its existence, is made perfectly clear in this introductory

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the

FIG. 1.-The Essex Museum of Natural History, Romford Road, Stratford, Essex.

new laboratories at Liverpool, Manchester, the Royal College of Science, and the McGill University at Montreal, to say nothing of the historic laboratories in our two ancient universities, would contain much to interest those inhabitants of India to whom Prof. Küchler's report appeals, while in many respects, specially, perhaps, in the organisation of the practical work for large classes, the arrangements in the English laboratories seem to have the advantage.

In dealing with the last part of his subject, the construction and standardisation of instruments, Prof. Küchler again rightly directs attention to the important services rendered to German industry by the Reichsanstalt and the disadvantages under which English manufacturers find themselves from the incomplete equipment of the National Physical Laboratory.

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chapter. As the author says, there is in Essex no other organised scientific body having the same or similar aims."

The actual scientific achievements of the club were fully set forth in an address delivered by Prof. Meldola at the annual meeting in 1901. As regards publications, the output has been not only large in quantity, but, what is more to the point, excellent in quality and strictly appropriate to the functions of a local society. Five volumes of Transactions and Proceedings were published down to 1887, after which the official publication was named the Esser Naturalist. The fourteenth volume of the latter is

1 Yearbook and Calendar for 1905-6." Edited by William Cole. (TH Club's Headquarters, and Simpkin, Marshall, Hamilton, Kent and Co, Ltd! Price 18

2 The Coming of Age of the Essex Field Club" (cor) Copies can le obtained on application to the Hon. Librarian, Mr. T. W. Reader, Es Museum, Romford Road, Stratford, Essex.

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now in course of publication. In addition to the above periodicals, three special memoirs" have also been issued, and it is hoped that others will be added from time to time. In 1885 appeared Prof. Meldola's and Mr. White's Report on the East Anglian Earthquake of 1884," in 1890 Mr. Miller Christy's "Birds of Essex," and in 1898 Mr. Henry Laver's "Mammals, Reptiles and Fishes of Essex." All these works were noticed in our pages at the time of publication. Four "museum handbooks" must also be credited to the club.

Not the least important part of the results achieved since 1880 is the establishment and maintenance of two museums, one of a strictly local character for the Epping Forest district at Queen Elizabeth's Lodge, Chingford, and the other of a county and educational character at West Ham in connection with, and attached to, the Municipal Technical Institute (see illustration). The first of these is carried on under an agreement with the Corporation of London, as conservators of Epping Forest. The other (county) museum was founded for the club by Mr. Passmore Edwards, and is maintained by the Borough Council of West Ham and the Essex Field Club, the library and headquarters of which are now in this same building. The personnel of the club as narrated by Mr. Christy is also of interest. The presidency has been held in succession by Prof. Meldola, Prof. Boulger, Mr. T. V. Holmes, Mr. E. A. Fitch, Mr. H. Laver, Mr. F. Chancellor, Mr. David Howard, Prof. Meldola, Mr. F. W. Rudler, and Mr. Miller Christy. All these are still living and active supporters of the club, while Mr. William Cole has acted as hon. secretary, editor of the publications, and curator of the museums during the whole twenty-five years of the society's existence.

There are few, if any, local societies in this country which can show such a good record. The Essex Field Club has earned the gratitude, not only of its own county, but of the world of field naturalists generally for the splendid example which it has set in showing how such organisations can keep alive the spirit of scientific research in the rural districts. In congratulating the club on its past achievements, we feel sure that the wish that its future work may be carried on with equal success will be cordially endorsed by all readers of NATURE.

THE MOSQUITOES OF PARÁ.'

N 1859, when H. W. Bates returned from Pará, the town, though rapidly improving even then, was still a little-known Brazilian port, and Bates embarked on a North American trading vessel, "the United States route being the quickest as well as the pleasantest way of reaching England.' At present, however, Pará is a very important place, and well up to date in scientific matters-if we may judge by the handsome publication before us, on one of the more recent branches of scientific inquiry--the transmission of yellow fever and other diseases by means of mosquitoes.

Four essays are included in the present volume, the first dealing with the mosquitoes of Pará regarded as a public calamity. This section is devoted to an historical sketch of the subject, the biology of mosquitoes, the views of various writers on the sanitary importance of the subject, and on the urgent need of practical efforts to abate the evil.

1 "Memorias do Museu Goeldi (Museu Paraense) de Historia Natural e Fthnographia." IV. Os Mosquitos no Pará. Reunião de quatro trabalhos sobre os Mosquitos indiger as, principalmente as especies que molestam.. homem. By Prof. Dr. Emilio Augusto Goeldi. With 100 figures in text and 5 chromo-lithographic plates. Pp. 154. (Pará, Brazil: Č. Wiegandt, 1905)

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