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certain even yet that anaërobic action is absolutely | as any in Southern Europe," to quote her description, necessary at any stage of sewage purification. Many | which is not exaggerated; she might have said " more other equally important questions might be instanced picturesque than," with reason." Away to the left are on which knowledge is still extremely limited.

the snowy heights of Lasithi, the hills above the skála The outstanding result of the Royal Commission's or landing-place of Ayios Nikólas, and distant rocky labours which will most appeal to local authorities Spinalonga, still the home of a peculiar race of is the statement that adequate purification can be Mohammedan fishermen-corsairs not so very long effected without land treatment, which, if recognised ago. To the right is the little isle of Psyrå, swimming by the Local Government Board, will remove what in the blue water. One would think that the is, in many cases, an impossible restriction. Their excavators on the monotonous plains of Babylonia, recommendation in regard to a central controlling / whose doings are chronicled by Prof. Hilprecht in the and advisory authority, if resulting in the creation last contribution to this volume, would have given of a department similar to the Massachusetts Board much sometimes to have been able to transport themof Health, may prevent great waste of public money. selves for a brief space to such goodly surroundings! Such a board might exercise wise discretion as to the Pachyammos lies a mile or so beyond, and east of amount of purification necessary under given con- | the scene of Miss Boyd's work, the low hill of Gournià. ditions. No central control, however, can be effective on which she has discovered the remains of a without efficient local management, and Mr. “ Mycenæan,” or more correctly " Minoan," town, a Thudicum's little book of simple methods of sewage | Bronze age settlement. It is a small Pompeii. One analysis will be of great assistance to local engineers

can walk up the sinuously curving little main street and intelligent works managers, and will help to

and look right and left into the ruined houses of the lighten the work of the trained specialist, with whom Bronze age “ Minoans.” There is even a sort of the solution of difficulties ultimately rests. G. J. F.

court-house or “palace," to give it the stereotyped

appellation, with its right-angle of low steps quite on AN AMERICAN CONTRIBUTION TO

the model of the splendid right-angled stairways of

Knossos and Phaistos, which Dr. Evans considers to ARCHÆOLOGY.

have been theatres, the prototypes of the stepped Greek University of Pennsylvania: Transactions of the

theatres of the classical period. This “palace" must Department of Archaeology: Free Museum of

have been the official centre of the town. Formerly, Science and Art. Vol. i. Parts i. and ii. Pp. 125.

judging from classical analogies, one talked of a prince (Published by the Department of Archæology, 1904.)

or “dynast” ruling from every one of these little THE most important article in this volume is the

palaces over his own little módus or city-state; but it 1 description of the American excavations at { will probably eventually be found that the ruler who Gournià, in Crete, which have already been referred | lived in such a “ palace" as that of Gournid was no to in the pages of NATURE (September 15, 1904, p. 482). | more than a mere mayor or demarch, a member of Miss Harriet A. Boyd, the leader of the expedition, an official bureaucracy analogous to that of ancient gives a full and very interesting description of Egypt, dependent upon the metropolitan authorities at her work, illustrated by photographs which give | Knossos. It becomes more and more probable that the reader a very good idea of the beautiful scenery | Crete in Minoan days was a homogeneous and highly of the Gulf of Mirabello (well bestowed name !), organised State like Egypt, not a mere congeries of a on the shores of which she found her work. No more hundred warring villages, as in classical times. delightful spot for archæological exploration could be | The official centre was not the religious centre of the imagined. Leaving the rather arid and uninteresting town. The cathedral of Gournià stood in the middle Candiote shore, near which Knossos lies, dominated l of the town, and was approached by a special street of by the towering hill of luktas, on the top of which, lits own so legend says, the god Zeus died and was buried, the

“ Not imposing as a piece of architecture," writes traveller skirts the base of the Lasithiote mountain

Miss Boyd (p. 41), “it is yet of unique importance as mass and reaches the narrow isthmus of Hierápetra

being the first Mycenæan' or 'Minoan shrine dis(the ancient Hierapytna). Before him rises a magnifi covered intact. The worshipper ascended three steps cent rocky wall of mountain, Thriphte by name, behind and through a doorway 1.50 m. wide entered an which is the peak called the Aphendi, or Lord of, | enclosure, about 3 m. square, surrounded by walls half Kavoúsi, the village which lies at its foot. This wall a metre thick and 50 to 60 cm. high. The floor is of

beaten earth.” is rent by a mighty cleft, the chasm of Thriphte, which is one of the dominating features of the landscape. The more noteworthy of its contents are Along the base of the wall runs the high-road from a low earthen table, covered with a thin coating of Kavoúsi to Hierápetra across the isthmus, which is plaster, which stands on three legs and possibly served low-lying land, forming a complete break in the as an altar, four cultus vases bearing symbols of mountain-backbone of Crete. On the northern shore

Minoan worship, the disc, consecrated horns and

double-headed axe of Zeus, a terra-cotta female idol of the isthmus is a good beach, Pachyammos (“ Deep

entwined with a snake, two heads of the same type as sand '') by name; in the centre of it the traveller will

1 Very curiously described as "A Lecture delivered before German Court see a large white house.

and University Circles, by H. V. Hilprecht." In it Prof. Hilprecht tells us This was Miss Boyd's headquarters. All around are little or nothing about the excavations at Nippur that has not already

appeared in his "Explorations in Bible Lands, and the photographs pub splendid mountains and “a coast-line as picturesque lished are already well known to archæologists.

the idol, several small clay doves and serpents' heads, | than he will spend wisely on the one useful article in a all of coarse terra-cotta, and a fragment of a pithos, on thousand; one is tempted still more to wish that a which a double-axe and disc are modelled in relief.” rigorous technical censorship might be instituted which

This important find has since been paralleled by Dr. would allow nothing to find its way into print but that Evans's discovery at Knossos of a similar shrine of the which was of permanent value to the world. In this snake-goddess with fine glazed faïence figures, re- way the amount of technical literature might be ferred to in NATURE (vol. lxx. p. 482). But Miss Boyd | brought within reasonable limits by being reduced to, was the first to discover the Minoan snake-goddess, of say, one-tenth of its present volume. whose existence we had no inkling before the excav If this is true of the matter which is published in ations at Gournià.

journals—which has, at least as a rule, the merit of Another good find, of which Miss Boyd gives a fine originality-it is still more true of the matter which facsimile plate, was the head of a bull in terra-cotta, appears in the form of technical text-books. We a typically “Mycenæan" object, paralleled by the imagine these books find a ready sale, else we cannot famous silver bull's head found by Schliemann at | account for their publication ; yet we do not know by Vycenæ, and the Egyptian representations of golden whom they are read except the reviewers. This is protomae of bulls being brought as gifts to the court exemplified by the six volumes before us, all of which of Thothmes III. by the Mycenaean (or rather have appeared within the last few months. With the ** Minoan ") ambassadors from “ Kefti” (Crete). exception of the first two, we would venture to say that

Miss Boyd's work has contributed results to it would have been just as well, and possibly even Mvcenæan lore which are of the highest importance, better, had they not been published. We do not mean results upon which the officers of the American Explor- | thereby that they are bad books, though one of them ation Society at Philadelphia, which dispatched her we think, should not be left about where young elec**Xpedition, are to be heartily congratulated.

tricians might see it; but they are not of merit enough H. R. Hall. | to justify the expense of their publication or purchase.

Take, for example, Miss Zimmern's little volume; it

is tastefully bound and clearly printed on good paperELECTRICAL THEORY AND PRACTICE. there is something in its appearance strongly suggesMaxwell's Theory and Wireless Telegraphy. By H. tive of a book of minor poetry. Add to this that it is

Poincaré and F. K. Vreeland. Pp. xi +255. (Lon- pleasantly written and that there is nothing very don: A. Constable and Co., Ltd., 1904.) Price seriously wrong with its statements, and its merits are fos. 6d, net.

summed up. On the other hand, we are confident that Alternating Currents. Vol. i. By A. Russell. Pp. it would fail in its object of explaining the complex

xii + 407. (Cambridge: The University Press, 1904.) theories of modern electricity to the “ general reader "; Price 125. net.

he might put down the book with the feeling that his IT'hat Do We Know Concerning Electricity? By knowledge had been increased, but it would be a mis

Antonia Zimmern. Pp. vii + 140. (London : taken notion. It requires genius of a very rare kind, Methuen and Co., n.d.) Price is. 6d. net.

such as was shown by Faraday in his “ Chemical HisVodem Electricity. By J. Henry and K. J. Hora. tory of a Candle," or by Prof. Perry in his “ Spinning

Pp. 355. (London: Hodder and Stoughton, 1905-) | Tops," to write a book of this kind; we intend no disPrice 5s. net.

paragement to the writer of this volume by saying that Modern Electric Practice. Vol. v. Edited by M. | such genius is not shown in it. Maclean, Pp. vi + 287. (London: The Gresham Messrs. Henry and Hora's volume is of another Publishing Co., 1904.) Price gs. net.

stamp; in a preface which reads like a publisher's Electricity Control: A Treatise on Electric Switch-Gear advertisement, the authors state that “the work will Systems of Electric Transmission. By Leonard be found eminently practical, scientific, and accurate." Andrews. Pp. xv +231. (London : Chas. Griffin and we have found it quite the reverse, and feel sorry Co., Ltd., 1904.)

for the “ apprentice” or “artisan " who “ gains a THE electrical engineer who wishes to keep pace complete knowledge of the fundamental principles of T with the development of his profession and de electricity” from its pages. This is a book which no sires to know something more than that which con self-respecting electrical censor, however lenient, would cerns only the particular branch in which he is engaged have allowed to appear in print. has a very hard task before him at the present day. He ! The two last books on the list are not without merit must, in the first instance, endeavour to keep an eye or value, but it is at best of an ephemeral kind. Of in the technical literature-the innumerable journals “ Modern Electric Practice " we have already expressed and proceedings, the monthly magazines, and the our views in writing of the previous volumes; the preweekly papers-of at least four countries in three dif. sent one does not depart from the same high standard ferent languages. This is in itself a task of no mean in production, and the three articles in section iv., dealdifficulty, which is heightened rather than diminished ing with boilers, engines, and auxiliary plant, are well by the various "abstracts " available. So rapid is the written and well illustrated. The article on electromultiplication of journals and papers that one is chemistry and electrometallurgy is less satisfactory. tempted to think that the best advice to give a student We must confess, however, that the inaccuracies would be to read nothing, as if he tries to read much noticed in previous volumes make us, unjustly perhe will waste more time over what is of no value to him haps, suspicious of the figures and data in the one be

fore us. Mr. Andrews's book on “ Electrical Control " branches except to leeward, but similar subjects are is a descriptive treatise on switch-gear. It possesses

accessible to most botanists, and for this reason they

do not possess the interest attaching to photographs the same disadvantages as “Modern Electric Prac

from less accessible countries. The names of several tice"; one cannot learn electrical practice from a book;

new contributors are announced, among them Mr. E. there is only one school—the practical school—in which Ule, whose character sketches of epiphytes in the one can learn the principles and details of construction | Amazon region of Peru appear in the first part of this of apparatus in one-tenth of the time and ten times as series. Of the Cactacea, which are widely spread thoroughly as by means of written descriptions. Prac

through South America, a number of genera include

epiphytic species, and in this region Cereus is pretical men are apt to complain that text-books are value

dominant. Cereus megalanthus, a species which less, as they are written by theorists; we have read a might be called a climbing epiphyte, is shown perched great many text-books of late written by practical men, on a Ficus tree. Another curious condition is that of a and have come to the conclusion that it is only the flourishing bromeliad, Streptocalyx angustifolius, theorist who should write them. He can describe the where, according to the writer, the exuberance of vege

tation is so directly traceable to ants that he compares underlying principles which persist when the fashion

the phenomenon with the fungus gardens described a of their application alters; the practical man describes

few years ago by Dr. A. Moeller. The last part of the the methods of his practice which even as he writes

series contains photographs taken in the Italian become antiquated.

colony of Eritraea by Dr. Schweinfurth. Hyphaene We have reserved to the last the two volumes which thebaica, the doum palm, familiar on account of its

branching habit, the sycomore fig, and an arboreous head our list. Messrs. Poincaré and Vreeland's book de

Euphorbia are among the characteristic specimens serves a place in any electrical library on account of its

chosen to illustrate different regions in the country. remarkably simple and lucid explanation of Maxwell's theory and of the work of Hertz, Lodge, and others

Author and Printer. An Attempt to Codify the best which led to the development of Hertzian telegraphy.

Typographical Practices of the Present Day. Bu

F. Howard Collins. Pp. XV + 408. (London: This is from the pen of M. Poincaré, translated by Mr.

Henry Frowde, 1905.) Price 5s, net. Vreeland, and forms the first part of the book. The THE want of uniformity of spelling, capitalisation. second part, written by Mr. Vreeland, deals with the

punctuation, and use of italic type causes continual problems presented by the practice of wireless tele trouble to all who are responsible for the editorial graphy, and the writer, by wisely confining himself to supervision of scientific literature in any form. Some

authors are more German than the Germans in their principles rather than details, has succeeded in writing

use of capitals, while others underline their manua worthy sequel to M. Poincaré's work.

scripts as freely as ladies do their correspondence. It Mr. Russell's book is the first volume of a mathe

is frequently difficult to decide questions of orthomatical treatise on alternating currents. Alternating graphy, and to reduce individual practice to the concurrent machinery is growing so steadily in import

sistent style, which is desirable in the columns of a ance, and the mathematical theory in connection with periodical, but is not always maintained. Mr.

Collins has prepared his book to help in this end, as it is so complex, that there is plenty of room for a

a standard guide for “Authors, Editors, Printers, thorough and comprehensive work of this kind. The

Correctors of the Press, Compositors, and Typists." present volume deals with the general theorems, and The volume contains more than twenty thousand the second will be devoted to the more specific theory separate entries of words arranged alphabetically. of alternating current machines and the transmission Included among these are abbreviations, disputed

spellings, foreign words and phrases, divisions of


words, and various rules and explanations which

should prove of service to authors and editors. The OUR BOOK SHELF.

proofs of the work have been read by many writers

and others who can give authoritative opinions as to Vegetationsbilder. Edited by Dr. G. Karsten and H.

what is correct or customary, so that the book does Schenck. Second series. Parts i.-viii. (Jena :

not contain merely Mr. Collins's decisions, but a conGustav Fischer, 1904.)

sensus of opinion edited by him. The first series of the “ Vegetationsbilder ” met with well-merited success, and a second series has been Highways and Byways in Derbyshire. By J. B. appearing at intervals during the past year. Of the Firth. With illustrations by Nelly Erichsen. contributors to the first series, Drs. G. Karsten and E. (London: Macmillan and Co., Ltd.) Price 6s. Stahl have again supplied material, the former taking With this book as a guide, a tourist could spend up a never-failing source of interest in the mangrove many pleasant weeks in Derbyshire, and he would vegetation, whilst Dr. Stahl, in a double part, deals learn that every part of the county has literary and with the xerophytes and conifers of Mexico; amongst historical associations of great interest. But while the the latter the primeval Taxodium trees growing in human side is so well represented, little notice is taken the park of Chapultepec and the sombre cypresses on of nature, except from the æsthetic point of view. the road to the sacred mount of Amecameca bear the “Of natural history and geology," says the author, impress of historic antiquity. Another number, con- " there is frankly nothing in this book, of science sisting of parts v. to vii., is devoted to the representation, nothing, of sport nothing." of mid-European forest trees, in accordance with an Notwithstanding this confession of what we may be expressed desire for subjects taken from native sources. permitted to describe as sins of omission, notes and The photographs taken by Dr. L. Klein include typical descriptions of places in which scientific readers are specimens of conifers and beeches in the Schwarzwald particularly interested occur here and there. For and Switzerland, and others showing the changes instance, a short account is given of the stone circle wrought by browsing aniinals and devastating winds; of Arborlow, the Stonehenge of the Midlands. The many of them are excellent, notably a scene of wind- monument consists of a circular enclosure in which blown pines which have been entirely cleared of are a number of blocks of limestone, all lying flat on

the ground in a rude circle, while at the centre are Introductory Mathematics. By R. B. Morgan. large blocks which probably formed the central dol- | Pp. vi+ 151. (London : Blackie and Son, Ltd., 1905.) men. "There are two entrances to the enclosure, a Price 2s. northern and a southern, and on the east side of the In Mr. Morgan's “ Introductory Mathematics " the latter is a large detached mound. Four hundred yards view of the author is that as soon as a boy knows west of the main enclosure is a still larger mound, decimal and vulgar fractions he should begin a mixed known as Gib Hill, connected with it by a low course of elementary practical mathematics comprisrampart of earth, now nearly worn away." Buxton ing algebra, geometry, and squared-paper work, and Matlock lead Mr. Firth to make some quotations developed as a whole in mutual dependence, leading up from Erasmus Darwin's poetical references to them in through the manipulation of formulæ to the solution his " Botanic Garden : Economy of Vegetation," and of problems involving simultaneous simple equations ** Loves of the Plants." Dr. Darwin knew and loved and giving a knowledge of the fundamental facts of the scenes he described, whatever opinion may be geometry with a training in practical applications such held as to his possession of the divine afflatus. There as the plotting of graphs and of figures to scale, and are a few other references to people and scenes of the finding of simple areas and volumes. This scheme, especial interest to the scientific world, but the book | ignoring the old water-tight compartment system, is will not be valued for these so much as for its bright a good one. The chapters on algebra and geometry narrative of literary and historical centres of Derby usually alternate, and the work progresses on natural shire, and its fine illustrations.

and easy lines, with illustrations of every day interest.

The author might with advantage have carried the idea The Tower of Pelée. New Studies of the Great still further and have brought in computations from

Tolcano of Martinique. By Prof. Angelo Heilprin. quantitative experimental work in the laboratory, inPp. 62 + xxii plates. (Philadelphia and London : volving the use of the balance and measuring flask, and Lippincott, 1904.)

perhaps an investigation of the action of forces at a PROF. HeilPRIN's latest volume on Martinique is point. There are some minor defects, such as an chiefly remarkable for the beautiful photographic occasional lack of precision in a statement, bad perplates with which it is illustrated; they give an spective in several of the figures, the use of a graph excellent idea of the features of the great tower of to give a forecast of population fifty years hence, &c.

olid lava which for nearly three years has been the But the treatment of the subject as a whole is very centre of interest in the crater of Pelée. One of satisfactory; there is a good collection of exercises, and these plates, however (No. xi), seems to have been the book is well suited to its purpose. accidentally printed upside down. In the accompanying text there is an account of the author's fourth visit to the volcano in June, 1903, and a good deal

LETTERS TO THE EDITOR. of somewhat discursive matter regarding the lessons

(The Editor does not hold himself responsible for opinions to be learnt from the recent eruptions. The number

expressed by his correspondents. Neither can he undertake of points which are still unsettled concerning the

to return, or to correspond with the writers of, rejected mechanism of the explosions and the concomitant

manuscripts intended for this or any other part of NATURE.

No notice is taken of anonymous communications.) phenomena is very large, and the author shows a wise caution in dealing with some of them. He advances

The Dynamical Theory of Gases and of Radiation. the opinion that the tower of Pelée is a volcanic core LORD RAYLEIGH, in a letter which appears in NATURE of ancient consolidation, and not an extrusion of

of May 18, opens up the general question of the applicsolidified new lava, as the French observers believe.

ability of the theorem of equipartition to the energy of We cannot believe this is at all likely to obtain general

the ether. As the discussion has arisen out of my acceptance.

" Theory of Gases," may 1, by way of personal explanJ. S. F.

ation, say that although I was fully alive to the questions Experimental Researches on the flow of Steam

referred to in this letter when writing my book, yet it Through Nozzles and Orifices. By A. Rateau.

seemed to me better not to drag the whole subject of Translated by H. Boyd Brydon. Pp. iv + 76. (Lon

radiation into a book on gases, but to reserve it for subdon: Constable and Co., Ltd., 1905.) Price 4s. 6d.

sequent discussion? Since then I have written two papers

in which questions similar to those raised by Lord Raynet.

leigh are discussed from different aspects, but as neither The laws of flow of steam are of much importance in of these papers is yet in print, I ask for space for a the design of turbines. A clear sketch is given of the short reply explaining how my contentions bear on the theory, and then an account of an excellent experi. special points raised by Lord Rayleigh's letter, mental research to determine the values of the con May 1, in the first place, suggest that the slowness with stants. Amongst previous experiments, those of

which energy is transferred to the quicker modes of etherSapier are English, not American as the author states.

vibration is a matter of calculation, and not of speculaThe novelty in M. Rateau's method is the use of an

tion? If the average time of collision of two molecules ejector condenser for condensing the steam.

in a gas is a great multiple N of the period of a vibra

The rise of temperature, which is easily measured, gives the

tion, whether of matter or of ether, then the average

transfer of energy to the vibration per collision can be quantity of steam condensed. The errors of the

shown to contain a factor of the order of smallness of method, especially that due to entrained water, are e-N. The calculations will be found in SS 236-244 of carefully examined. Convergent nozzles and a thin my book. It is on these that I base my position, not on plate orifice were used. The results are compared with a mere speculation that the rate of transfer may be slow. thos by Hirn on air, and close agreement is found. Lord Rayleigh's example of a stretched string. saya In a note, the complex phenomenon of the discharge / piano wire, will illustrate the physical principle involved. of hot water just on the point of evaporating is

if a piano hammer is heavily felted, the impact is of long t'xamined.

duration compared with the shortest periods of vibration, The translation is clear. It is, however, a defect, for

so that the quickest vibrations are left with very little English readers, that the principal formulæ are left as

energy after the impact, and the higher harmonics are given by the author in foreign units.

not heard. If the felting is worn away, the impact is of The book is

shorter duration, the higher harmonics are sounded, and essentially one for practical use, and it would have

the tone of the wire is “ metallic." added much to the convenience of engineers if other The factor e-N is so small for most of the etherformulæ than the one on p. 6 had been given in English vibrations as to be negligible. There is no sharp line of units

| demarcation between those vibrations which acquire energy very slowly and those for which the rate is appreciable; | vibrations in the ether. But if the face of the thermobut as e-N varies rapidly with N when N is large, there pile is of lampblack, the atomic motions in lampblack at will be but few vibrations near the border, so that it seems 600° C. may not be of sufficient rapidity (mainly, so far as legitimate, for purposes of a general discussion, to divide can be seen, on account of the lower elasticity of the the vibrations into the two distinct classes, quick and material) to excite red vibrations except as a kind of slow, relatively to the scale of time provided by molecular equilibrium tide,” in which case the lampblack will not collisions.

emit red radiation. When the material bodies are solid, the physical prin I cannot ask for further space in which to answer Lord ciple is the same, the relatively slow motions of the atoms Rayleigh's point as to the enclosure with a hole in it, but affecting the “ quick” vibrations of the ether only by I have discussed a similar question in a paper which I raising a sort of “ equilibrium tide."

hope will soon be published, in connection with Bartoli's The number of “ slow” vibrations of the ether in any proof of Stefan's law. I hope that this paper, and a finite enclosure is finite. These quickly receive the energy second one which is at present in the hands of the printer, allotted to them by the theorem of equipartition. Thus will explain my position more clearly than I have been they form the medium of transfer of radiant energy able to in the short limits of a letter. between two bodies at different temperatures. After a May 20.

J. H. JEANS. moderate time the slow vibrations have each, on the average, energy equal to that of two degrees of trans

Fictitious Problems in Mathematics. lational freedom of one molecule; the quick vibrations have no appreciable energy, while the intermediate vibra I HAVE to thank your reviewer for so readily supplying tions possess some energy, but not their full share. It (NATURE, May 18, p. 56) the example to prove his contenis easily seen that the number of slow vibrations is tion-and which appears (to me) to disprove it. approximately proportional to the volume of the enclosure, The man who set that example did so in order to test so that roughly the energy of ether must be measured

(inter alia) whether the pupil knew that, for any friction per unit volume in order to be independent of the size of

| to arise, both the surfaces must be rough; your reviewer the enclosure. For air under normal conditions, I find as

originally wrote :-" What the average college don forgets the result of a brief calculation that this value is of the is that roughness or smoothness are matters which conorder of 5 x 10-' times that of the matter. The law of

cern two surfaces not one body." The italics are your distribution of this energy will be

reviewer's; and this is the statement which I called (and

still call) in question. 01-*da

It is no part of my book to uphold the verbiage in until we arrive at values of which are so small as to

which the example is couched ; by chance, in my former be comparable with

letter, I explained in anticipation the terms used in it. I velocity of light

do not see, however, why your reviewer applies the radius of molecule x

favourite word inaccurate to these terms. Perfect smoothvelocity of molecule

ness may not occur in nature; still, in considering the After these values of are passed, the formula must be pendulum, I probably begin by assuming no friction on modified by the introduction of a multiplying factor which the axis of suspension, and, if I try afterwards to apply falls off very rapidly as a decreases, and which involves a correction for this friction, I probably make an assumpthe time during which the gas has been shut up. It is tion which is inaccurate. Friction = pressure x a constant easily found (cf. The Dynamical Theory of Gases," is inaccurate, statically and dynamically. $ 247) that at o° C. the spectrum of radiant energy is

C. B. CLARKE entirely in the infra-red; at 28,000° C. it certainly extends to the ultra-violet, and probably does so at lower temperatures.

As I take it, the mathematician's “ perfectly rough Finally, Lord Rayleigh asks :

body" means a body which never by any chance slips on Does the postulated slowness of transformation really any other body with which it is placed in contact, similarly obtain ? Red light falling upon the blackened face of a

the “ perfectly smooth body" is supposed never to offer thermopile is absorbed, and the instrument rapidly in any tangential resistance to any other body which it dicates a rise of temperature. Vibrational energy is

touches. The inconsistency of this nomenclature is evident readily converted into translational energy. Why, then,

when we imagine the 'two bodies placed in contact with does the thermopile itself not shine in the dark?"

each other, as in the case of the perfectly rough plank Before trying to answer this, I wish to emphasise that

resting on the smooth horizontal plane. The subsequent my position does not require the forces of interaction

course of events cannot at the same time be compatible between matter and ether to be small. Considering a gas

with the assumed perfect roughness of the one body and for simplicity, the transfer of energy per collision to a

the assumed perfect smoothness of the other. The covibration of frequency R is found to be proportional to the efficient of friction between two bodies depends essentially square of the modulus of an integral of the form (cf. “ The

on the nature of the parts of the surfaces of both bodies Dynamical Theory of Gases,” $ 237)

which are in contact as well as on their lubrication, and

neither body can be said to have a coefficient of friction f(t)erede,

apart from the other. It is equally incorrect to speak of

perfect smoothness or perfect roughness as attributes of a where f(t) is a generalised force between matter and ether. single body. Moreover, this misleading language is quite The integral may be very small either through the small unnecessary; it is very easy to frame questions in a way ness of f(1) or the largeness of p. I rely entirely on the that is free from objection. For instance, “A man walks largeness of p, because calculation shows this to be without slipping along a plank which can slip without adequate. The thermopile experiment gives evidence as to friction on a horizontal table:" Or again, " A sphere is the magnitude of f(t), but this does not alter the fact that placed in perfectly rough contact with the slanting face the integral is small for large values of p.

of a wedge whose base rests in perfectly smooth contact This being so, I am afraid I do not very clearly under | with a horizontal plane."

G. H. BRYAX. stand why the thermopile should be expected to shine in the dark. If the red light is a plane monochromatic wave, its energy represents only two coordinates of the ether,

A New Slide Rule. and has to be shared between the great number of co In the article which appeared on p. 45 of NATURE, ordinates, six for each atom, which belong to the thermo- May 11, describing the Jackson-Davis double slide rule. pile. If the red light comes from a large mass of red vou notice one little fault in the rule sent for examination. hot matter inside the same enclosure as the thermopile, We desire to exonerate the designer of the instrument, then the thermopile will soon be raised to the tempera- | Mr. C. S. Jackson, from responsibility for the very obvious ture of this mass, and may shine in the dark. If the hot | fault to which you allude, viz. that the scale on the feather mass consists of iron, say at 600° C., the atomic motions edge is divided into inches and sixteenths, and that the in the iron must be sufficiently rapid to excite the red continuation scale which is read below the ordinary slide

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