simultaneous equations; they are not baffled by the occurrence of huge coefficients in the course of elimination, and contrive to solve equations of incredibly high degrees. Finally, the elegant designs of familiar things, such as toys, fans, etc., suggested equally elegant problems of a quite distinctive kind, such as the Gion Temple problem, an account of which is given, pp. 197-8. The first solution involved an equation of degree 1024, which was successively reduced (we are told) to 46 and 10 the last by Ajima, who seems, so far as we can judge, to have been the greatest mathematician of his nation up to the present time.

The fourteen chapters of this book are all interesting, but we can only point out a few of the topics. There is an excellent account of the way of using sticks and abaci for calculation, and of the early system of notation; this is followed by showing how the same implements were used to solve equations, after the manner of Horner. Coming now to the third period (1600–1675 or so) we have circle-rectification of an Archimedean type, magic squares and circles, and something like a theory of quadrature. Seki Kōwa is the leading figure of the time, and chapter vi. is entirely devoted to him, and gives abundant evidence of his talent and ingenuity. The authors, however, class him rather with C. Wolf or Barrow than with Newton or Leibnitz. Chapter vii. deals with Seki's contemporaries and the probable importation of some western mathematics through contact with the Dutch.

Chapter viii. is on the yenri, or "circle principle." Practically, this means the formulæ connected mainly with cyclometry, some of which are essentially infinite series such as we have in analytical trigonometry (cf. for instance, pp. 152-3). Matsunaga worked out to 50 figures in the eighteenth century.

Of the remaining chapters the most notable is that on Ajima Chokuyen (1739–1798). Among his achievements may be mentioned his (analytical) solution of Malfatti's problem, and his anticipation of Steiner by discovering poristic rings of circles touching each other and two given fixed circles. He also dealt with repeating decimals, diophantine problems, and quadrature; in the last he comes nearer than any of his predecessors to the idea of a definite integral as the imit of a sum. He may possibly have been nfluenced by European work.

A special feature of the book is the large number of illustrations. Those which are diagrams for problems are always elegant and often emarkably beautiful (e.g. pp. 96, 185, 186, 198, 40, 245); others are very instructive, like those of the abaci, pp. 30-31.

We cannot help asking ourselves: What is likely to be the trend of Japanese mathematics for the next generation or so? Japanese students are now made acquainted with the vast structure of European mathematics, and it is too massive and too much based upon the fundamental nature of things for them to ignore. If they are to add to it, they must become acquainted with it, unless they go on making pretty little things that the master-builders will put into their proper place. But it would be a great pity if, in striving to contribute to the substantial parts of the building, the Japanese were to bury their special talents, innate sense of asymmetrical beauty, and exceptional endurance and power of taking pains. Such things as on one hand celestial mechanics, and on the other diophantine analysis, seem admirably suited to their genius; if there be a planet of the solar system beyond Neptune, or if there be a proof of Fermat's last theorem, a Japanese is as likely to discover it as anyone. G. B. M.

PRACTICAL EDUCATION.

(1) A Handbook of Vocational Education. By Dr. J. S. Taylor. Pp. xvi + 225. (New York: The Macmillan Co.; London: Macmillan and Co., Ltd., 1914.). Price 4s. 6d. net. (2) A Class-Book of Commercial Knowledge. By E. J. Balley. Pp. iii+125. (London: G. Bell and Sons, Ltd., 1914.) Price 1s. 6d.

(1) THE

HE aim of Dr. Taylor's book is to give "a systematic survey of the general field of vocational education, embodying both the historical and logical aspects of the subject." But the author has not done full justice either to the subject or to himself by the short summary he has produced. With the introduction, pleading for equal opportunities for all, for education for citizenship, for a due recognition of the bearing of the industrial revolution on the teaching of trades, English opinion will be in full sympathy. So, too, with later chapters insisting on the need for guidance in the choice of an occupation, and on the part that trade schools should play in making good the loss of the thorough, all-round training afforded by the old apprenticeship system at its best. But the historical account of industrial education in Europe, given in chapter ii., is far too sketchy to be of real value.

Germany, and in Germany the admirable continuation school system of Munich, designed and built up by Dr. Kerschensteiner, holds pride of place, and the constructive side of Dr. Taylor's book may be said to be based on Dr. Kerschensteiner's principles. In his whole-hearted devotion to this master, who has exhibited in rare

combination the talents of administrator as well as teacher, he forgets how much of Dr. Kerschensteiner's success is due to conscription. It is a conscript army that has rendered possible conscript continuation schools, and the iron discipline of the whole system of higher education in Germany. The essential condition of reform in continuation school work in Great Britain and in the United States is to secure there, as has been done in most German States, that young persons who have left the elementary school and gone to work shall continue their education in day, not night, classes. But the hope will be nursed on both sides of the Atlantic that this end will be achieved by some milder political measure than conscrip

tion.

As regards the training of vocational teachers, few will refuse assent to Dr. Taylor's contention that "a teacher of trades must be expert in two arts the art of teaching and the art of some craft." Theorising on the subject, educationists tend to give excessive prominence to its pedagogic aspect. In practice they are forced to act like business-men, and to accept a working compromise.

The bibliography is quite inadequate. Perhaps the most notable omission is that of Dr. Stanley Hall's great work on "Adolescence." Even an American book should acknowledge the world's debt to that distinguished American philosopher.

(2) Few words are needed to commend Mr. Balley's "Class-book of Commercial Knowledge." It is an excellent little book, and should be of the utmost value in secondary schools where some introduction to commercial studies is at last being recognised as desirable. The form of the book is good, for it is planned like an up-to-date textbook on other secondary-school subjects, the examples are modern and business-like, the specimens of business documents bound up with the text are a pleasure to handle, and may even stir the imagination of a future captain of industry. The author has succeeded in his object, viz., to show that the subject of commerce is both educative and interesting. Bookkeeping proper has been wisely left alone, as a separate subject. In a new edition more might well be said in section iii., dealing with office work, on modern methods of card-indexing and filing.

OUR BOOKSHELF.

Świat I Czlowiek. By A. Heflich and S. Michalski. Vol. iv. Pp. 355. Second Edition. (Warsaw Published by the Editors, 1913.) Price 2 roubles.

UNIQUE in its kind and of broad educational value is a Polish publication organised in Warsaw some

years ago and edited from the beginning by Messrs. Al. Heflich and St. Michalski. The whole work, the aim of which is to help the self-educator in all the principal branches of scientific knowledge and scientific method, consists of three series: (i) "A Guide for Autodidacts," (ii) “Man and the Universe" (the universe in the light of the theory of evolution), and (iii) "The History of Thought." The recently-published second edition of vol. iv. of the second series contains a very interesting exposition of social evolution among animals and men, and of moral evolution, by Dr. L. Krzywicki, a thorough chapter on evolution of psychical life, by Dr. M. Borowski; further, an exposition of evolution in art, by Dr. W. Tatarkiewicz; and, finally, an inquiry by Dr. Fl. Znaniecki into the meaning of evolution of man and of the universe.

The present volume closes a large circle of ideas developed in the three first volumes which, after an introductory treatment of the concept of evolution in general, bring the (advanced) private student face to face with the facts and problems of universal and terrestrial evolution, of the evolu tion of plants, animals and man, of human civilisation, of language and economic life. The "Guide" proper (series I.) consists of several independent volumes covering the needs of the self-educator in the departments of mathematics, natural sciences, philology and history, sociology and law, and philosophy.

It may not be out of place to mention that the whole publication, which, since 1898, has been circulated in many thousands of cheap but beautiful volumes, is entirely supported by the Mianowski-Fund, a national institution of great social utility, and by the disinterested labours of the editors. L. SILBERSTEIN. Crystallography: an Outline of the Geometrica. Properties of Crystals. By Prof. T. L. Walker. Pp. xiv 204. (New York: McGraw-Hill Book Co., Inc.; London: Hill Publishing Co., Ltd.. 1914.) Price Ss. 4d. net.

THE theodolite form of goniometer was invented, and the advantage of determining the position of a face on a crystal by a pair of co-ordinate readings of a single setting was pointed out almost simultaneously by a German, Goldschmidt, and a Russian, Fedorov. The method had, however. been used some years before by an Englishman, Miller, but the posthumous paper in which it was used escaped general notice. It is, however, largely due to the teaching of Goldschmidt and the series of researches carried out by him and his pupils that the convenience of the two-circle measurement of crystals has become widely recog nised.

Prof. Walker is imbued with the Goldschmidt spirit, and essays in the volume before us to remove the reproach that no text-book on crys tallography written in the English tongue is based on that method. We think that his effort has The been crowned with but qualified success. discussion of the different classes of crystal sym metry and the types of symmetry characterising

each, which occupies the greater part of the book, follows the ordinary, old-fashioned lines, even to the use of the Millerian indices, and the author has wisely refrained from complicating the discussion by devising a brand new set of names for the several classes. The sections on the Goldschmidt method are, on the other hand, scattered throughout the book; it would have been wiser to collect them together and to have expanded them. The argument is incomplete. For instance, the fundamental property of the gnomonic projection, viz., that all zones are represented by straight lines, is very indefinitely stated, and not proved at all. Examples of working out crystals belonging to the six systems should have been included in the several chapters, instead of reprinting more or less fully at the end of the book a few original papers, in which the actual working is subservient to the interest of the particular research. For a full understanding of the Goldschmidt method the student must still refer to the original source.

We are informed that the Hill Publishing Co., Ltd., are the London publishers, but their name is not given on the title-page.

The

First Book of Physiology and Hygiene. By Gertrude D. Cathcart. Pp. vi+158. (London: Macmillan and Co., Ltd., 1914.) Price 1s. 6d. It is apparently the notion in certain educational circles that hygiene can be taught without a preliminary knowledge of the science physiology on which it is founded. If such an idea still lingers anywhere it will be immediately dispelled by a perusal of this attractive little book. author shows quite clearly that the laws of health are direct deductions from physiological principles. These are explained in clear, simple language, so free as possible from technical terms, and we can highly recommend the book as suitable for readers commencing the study of the subject, or for those who do not wish to take it up from the professional and medical point of view. Where so much is excellent, it seems ungracious to point out a serious mistake, the only one so far as can be ascertained; this is the erroneous statement that the red blood corpuscles are the carriers of carbon dioxide.

W. D. H.

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

The Density of Lead from Ceylon Thorite. LAST May, in conjunction with Mr. H. Hyman, I published the resuit of an examination of the relative atomic weight of a small specimen of lead, less than one gram, separated from a kilogram of Ceylon thorite, which showed a value rather more than a unit in excess of that found for a specimen of ordinary lead. I have since been engaged in extracting the lead from 33 kilograms of Ceylon thorite, which was first carefully sorted by hand, piece by piece, into

various grades. From the finest grade, consisting of 20 kilograms, about 80 grams of lead were obtained, in agreement with the percentage obtained by

analysis.

This specimen, and a similar weight of ordinary assay lead, have been carefully purified by identical processes, and finally obtained as metal, by fusing the oxide with cyanide, and repeating the fusion with the metal. The very porous castings so obtained were melted in a mercury pump vacuum in glass tubes with drawn-out jets, and cast into cylindrical graphite moulds in the vacuum, hydrogen to atmospheric pressure being then admitted, and the lead allowed to freeze from the bottom.

20

It was thought that a determination of the specific gravity would yield results of interest. It is to be expected that the atomic volumes of isotopic elements should be identical, so that, on this view, the densities should be in proportion to the atomic weights. The density of lead distilled in a vacuum was found, by Kahlbaum, Roth, and Siedler, to be 11.3415 (D%), and after pressing to 10,000 atmospheres, 11-3470. For the ordinary lead, prepared as above detailed, D was found to be 11-3465, as the mean of three determinations agreeing within 8 units in the last place, in good accord with that found for distilled lead. On the other hand, the value found for the specimen of thorite lead was 11.376, which is 0-26 per cent. greater, and higher than has been found previously in any trustworthy determination. The atomic weight calculated from the density, taking 207.10 as the figure for ordinary lead, is 207.64. It remains to be seen whether the constants of the lead will be altered by further purification, but one would expect that the effect of any possible impurity would be to decrease, rather than increase the density.

During the purification of the lead, bismuth was specially looked for, but, if any at all was present, its quantity was certainly less than one part in ten millions of the mineral. This seems to dispose of the speculation that bismuth is one of the end products of the thorium disintegration. On the other hand, I was surprised to find a perceptible quantity of iodine in the mineral, and separated between one and two grams, which Mr. J. A. Cranston is now examining. So far as the tests have yet gone, there seems to be a distinct trace, also, of thallium present.

FREDERICK SODDY. Chemical Department, Aberdeen University, January 30.

The Cause of Streaks upon Lath and Plaster Walls. In reply to Mr. Thomas D. Cope's letter in NATURE of January 21, it may be stated that he is correct in supposing that the best explanation of the streaks on the plaster he refers to is that they are due to the hot-air molecules driving the dust particles into contact with the plaster, and the colder the plaster the weaker is the power of the cold-air molecules next it to resist the deposition. This tendency of hot air to deposit its dust on cold surfaces can be seen in a very marked way in any house heated with hot water or steam. Wherever a hot pipe comes through a wall there will always be found a dirty vertical streak on the wall just above the hot pipe, caused by the stream of hot air rising from the pipe depositing its dust on the cold surface.

This action of hot air on cold surfaces accounts for the difference in cleanness of surfaces in rooms heated by open fires, and those warmed by hot air or by the so-called radiators, which do most of their heating by warming the air by contact. In a fire-heated room the furniture is principally heated by radiation, and, being warmer than the air, it repels the

dust; while if heated by hot air, the air heats the furniture, and in so doing deposits its dust on it. These remarks apply to the fine dust, and not to the larger particles which fall on the furniture, and do not adhere to it like the heat-deposited ones. Electric lighting keeps the ceilings much cleaner than gas. Much of this cleanness is due to the much lower temperature of the air rising from the electric bulb than from gas-lighting, but ceilings over electric lights show blackening, especially in smoking-rooms.

The cause of the streaks on plaster referred to by Mr. Cope may, however, be a little more complicated than stated above, because the plaster is porous, and some amount of diffusion will take place between the gases in the room and those at the back of the plaster, and as the laths will reduce the diffusion their action will, to some extent, aid their heat-conserving effect. The principal cause of the streaks would, however, appear to be the heat effect, as it will be generally found that, if the heating and other conditions are the same, the ceilings of the rooms on the top flat of a house are much more lath and beam marked than those underneath, owing to the upper surface of the plaster in the upper rooms being exposed to the cold air under the slates while the ceilings of the lower rooms are kept warmer by the rooms over them.

It is possible the difference in the plaster in the cold room referred to by Mr. Cope may be due not to any action of the water vapour, but to its condensation on the walls ingraining the dust into

them.

The reply to Mr. Cope's last question is, yes. A reversal of the phenomenon is quite simple, and has already been referred to. Any surface hotter than the air keeps free of dust; a surface placed in a smoky chimney, if it is hotter than the gases, gets no soot deposited on it. A paper bearing on the above subject, and entitled "The Formation of Small Clear Spaces in Dusty Air," appeared in the Trans. Roy. Soc., Edin., xxxii., part ii.

In my letter in NATURE of January 21, the date of a letter there referred to is given as March 16, 1913, which should have been March 6, 1913.

Ardenlea, Falkirk, January 26.

JOHN AITKEN.

THE cause of these streaks, which are also often to be seen on ceilings, appears to be due to the fact that bodies which are warmer than the atmosphere are surrounded by a "dust-free space," and that dust is battered upon surfaces which are cooler than the atmosphere.

The dust-free space has been described by Tyndall ("Dust and Disease," Royal Inst., 1870), Frankland ("Dust and Disease," Proc. Roy. Soc., vol. xxv., p. 542), Rayleigh (Roy Soc., December 21, 1882; NATURE, vol. xxviii., p. 139), Aitken (Roy. Soc. Ed., January 21, 1884) and Lodge and Clark (Phil. Mag., March, 1884, p. 214).

Recently I have discussed the question of the discoloration of walls and ceilings (the Engineer, July 3, 1914) in an article on the "Theory of the Radiator."

In the above papers your correspondent will find answers to the questions he puts. R. M. DEELEY. Abbeyfield, Salisbury Avenue, Harpenden, January 22.

has for its main thesis that Bacon was the first to formulate a theory of universal continuity; an incorrect hypothesis, it is true, but one which Prof. Duhem believes to have served the useful purpose of supplementing "the peripatetic theory of heavy and light" until the discovery of atmospheric pressure. This theory developed in connection with certain problematical phenomena of which this "experiment" is the chief and typical case. If there is suspended in air a vessel of water having a hole in the top and several narrow apertures in the bottom, no water will fall from it so long as the superior aperture is closed. Yet water is heavier than air, and according to the principle of Aristotle's physics should fall to the ground. Writers before Bacon, according to Duhem, explain this anomaly by saying that the fall of the water would produce a vacuum, and that a vacuum cannot exist in nature. But Bacon argues that a vacuum cannot be the reason why the water does not fall, because a vacuum does not exist; he then explains further that although by their particular natures water tends downwards and air upwards, by their nature as parts of the universe they tend to remain in continuity. Duhem holds that Bacon was the first to substitute this positive law of universal continuity for the mere negation that a vacuum cannot exist in nature (2).

Prof. Duhem supports his case by citation of Greek, Byzantine, and Arabian sources, and by use of writings of fourteenth-century physicists available only in manuscripts. But unfortunately for his main contention he has overlooked that remarkable little treatise, “Questiones naturales," which Adelard of Bath, Bacon's countryman, wrote more than a century before Roger penned his "Questiones naturales" (3). In Adelard's fifty-eighth chapter his nephew says-the work takes the form of a dialogue between Adelard and his nephew-"There is still one point about the natures of waters which is unclear to me." He then

asks his uncle to explain a water jar, similar to that just described, which they had once seen at the house of an enchantress. Adelard replies in his clear, easy style, so different from the scholastic discussion in Bacon's corresponding passages:

"If it was magic, the enchantment was worked by violence of nature rather than of waters. For although four elements (4) compose the body of this world of sense, they are so united by natural affection that, as no one of them desires to exist without another, so no place is or can be void of them. Therefore immediately one of them leaves its position another succeeds it without interval, nor can one leave its place unless some other which is especially attached to it can succeed it." Hence it is futile to give the water a chance to get out unless you give the air a chance to get in. Finally, Adelard not only thus anticipates the theory of universal continuity, he describes what actually occurs in the "experiment more accurately than Bacon or the other physicists cited by Duhem. "Hence it comes about that, if in a vessel which is absolutely tight above an aperture is made below, the liquid flows out only interruptedly and with bubbling. For as much air gets in as liquid goes out, and this air, since it finds the water porous, by its own properties of tenuity and lightness makes its way to the top of the vessel and occupies what seems to be a vacuum" (5).

LYNN THORNDIKE.
Western Reserve University, Cleveland,
Ohio, U.S.A.

(1) Edited by A, G. Little, Oxford, 1914.

(2) Bacon Essays, p. 266. "Le doctrine dont nous avons suivi le développement au travers des écrits de Roger Bacon semble bien lui appartenir en propre.

A peine, croyons-nous, en avait-il trouvé chez ses prédécesseurs un germe presque infime," etc.

(3) For the dates of Adelard's life and writings see C. H. Haskins in the English Historical Review, vol. xxvi., p. 491, and vol. xxviii., p. 515 (July, 1911, and July, 1913).

(4) Adelard elsewhere in the treatise explains that the earth, air, fire, and water which we see and feel are not the elements earth, air, fire, and water, but compounds.

(5) The following is the complete Latin text of the chapter. I have used both the printed edition in the British Museum, where the text is sometimes faulty, and the twelfth-century manuscript in the Eton College Library, which is possibly the autograph. The chapter heading reads, Quare ex vase pleno inferius aperto aqua non exeat nisi prius superius foramen aperiatur." The text then begins :

"Adhuc mihi de aquarum naturis quiddam dubitabile restat. Cum enim tempore ut scis iam preterito anum prestigiosam studio incantationis discende addissemus ibique anilibus imbuti sententiis nescio an sentibus aliquot diebus moraremur, eadem in domo vas quoddam mirabilis efficacie ad horas prandiles afferebatur. Quippe cum idem et superius et inferius perforatum multipliciter foret, aqua etiam ad manus abluendas infusa, dum minister aquarius superiora foramina pollice obturabat, nichil aque ab inferioribus emanabat, ablato a superiore pollice statim nobis circumstantibus per inferiora foramina aqua redundabat. Quod ego, ipsum prestigium esse putans, quid mirum, inquam, si anus dominica incantatrix est cum aquarius servulus monstra pretendat. Tu vero more tuo, quoniam incantationibus studiosus eras, minime illi rei vacare dignatus es. Nunc igitur quid de aqua illa sentis aperta; semper erant subteriora foramina et nichil tamen nisi ad aquarii arbitrium fluebat.

(A) Si prestigium id erat, nature potius quam aquarum violentia id incantatum est. Cum enim huius mundi sensilis corpus quatuor elimenta componant, ita ipsa naturali amore conserta sunt ut, cum nullum eorum sine alio existere velit, nullus locus ab eis tum vacuus sit tum esse possit. Unde fit ut, quamcito illorum unum a loco suo cedat, aliud absque intervallo eidem succedat, neque potest a loco cedere, nisi aliud quod substantiali quodam affectat amore possit ei succedere. Clauso igitur introitu succedentis frustra patebit exitus succurrentis, hoc itaque amore hac expectatione in cassum aquae reperies, nisi introitum aeri prestes. Haec enim, ut supradictum est, cum non pura sint, ita coniuncta sunt ut sine se esse non possint vel nolent. Unde fit ut, si in vase superius penitus integro inferius fiat apertio, non nisi cum intervallo quodam et quasi cum murmure liquoris fiat effusio. Tantus enim aer intercedit quantum inde liquoris exit, qui quidam cum ipsam aquam porosam inveniat innativa sibi et tenuitate et levitate penetrando superiorem vasis locum qui vacuus videtur occupat. LYNN THORNDIKE.

The Economic Status of the Blackcap.

IN NATURE of January 7 Mr. W. E. Collinge (for whose work I have the greatest respect) places the blackcap in his list of injurious birds. As at once a gardener and an observer of birds for about sixty years I wish to protest against this accusation, which, if acted upon by fruit farmers, would soon lead to the extinction of the most charming songster of all the true warblers.

I grant that it eats small fruits, especially raspberries, but I contend that the insects it destroys must, From the economic point of view, fully counterbalance hese depredations. This, of course, cannot be proved, because all the insects it devours are not injurious,

and the proportion of these will vary in each locality, but considering that the blackcap arrives in this country early in April and does not leave until September, while the season for small fruits lasts practically only from the beginning of July to the middle of August, we have about sixteen weeks when it has to live on insects to six weeks of fruit eating!

Mr. Collinge rightly says that the bird is "not plentiful" (p. 510), but adds that it has considerably increased in numbers during the last eight or nine years (p. 511). To this I must entirely demur-certainly as regards this part of Kent, where much small fruit is grown. It is a bird the clear melodious song of which cannot be overlooked, and as I have been on the look out for it every spring for the last thirty years at least, I am perhaps as competent to form an opinion on this point as Mr. Collinge. I have never more than one pair in my garden, and rarely hear the bird elsewhere. I should say it is not as abundant here now as it was twenty years ago at Colwyn Bay, where I then lived.

ALFRED O. WALKER. Ulcombe Place, Maidstone, Kent, January 26.

I REGRET quite as much as Mr. Alfred O. Walker to have to condemn the blackcap, but in an investigation of this kind one must always be careful not to allow sentiment or preconceived notions to bias one's opinion.

I have ample evidence that this bird has increased in numbers, at least in the midland counties, during the past six or seven years. I cannot speak for Kent. As to the nature of its food, an examination of the stomach contents of thirty-three adult and four nestling birds showed that the bulk of the food consisted of fruit and peas; there were a few aphids, twenty small lepidopterous larvæ, and the remains of seven beetles. Out-of-door observations made during the past ten years add still further evidence of the injuries these birds will inflict upon wall fruit, currants, strawberries, blackberries, raspberries, peas, etc. During the summer of 1913 I had ample proof in my own garden of the havoc four or five birds can commit on peas.

Mr. F. Smith, of Maidstone, a large fruit-grower and a careful observer, stated in a paper published in 1906-"A family of blackcaps in a cherry orchard commit grave havoc. They do not eat a quarter of the fruit they pick, and they are also very fond of raspberries and figs. It is the worst summer bird we have in the fruit plantations." This opinion has been confirmed by fruit-growers in all parts of the country.

Where this species is not plentiful or in non-fruitgrowing districts, it may be left alone, but in fruitgrowing districts it should not be allowed to increase, further, as I stated in 1913, "any attempt at protection will justify fruit-growers in taking vigorous measures for extermination."

WALTER E. COLLINGE.

8 Newhall Street, Birmingham.

Names in Mechanics.

In the current number of NATURE Sir Oliver Lodge refers to the usefulness of naming units, and many of us remember what a clearing up of ideas resulted in the student's mind from the substitution of the term "radian" for the circumlocution "unit of circular measure." I wish to ascertain any names that have been proposed for units in mechanics, and have attained little or no vogue; as instances "velo" and "celo" may be mentioned, which were proposed as names for the units of velocity and acceleration. I wish also to know how far Prof. Perry's "slug" is in use. Can any reader of NATURE help me? DAVID MAIR.