of "Volumetric Gas Analysis," are not exercises in the volumetric as contrasted with the gravimetric analysis of gases, but have to do with the analysis of solids and liquids by measuring the volumes of gas set free from them. In this section, for instance, are described the methods of estimating nitrates by the Lunge nitrometer and analogous processes. The book is presented in an attractive form, and carries out admirably the purpose of the author and translator to provide an introduction to the larger standard works on gas analysis.

(4) The German treatise on the theory and practice of the gas industry is a large work of which the present volume constitutes "I. Band, I. Halfte." It includes the historical development of the principles of mechanics and physics, and the fundamental laws of thermodynamics. The subjects treated include isothermal and adiabatic compression, change of state, evaporation and boiling, viscosity of gases and vapours, specific heats, entropy of water-vapour and vapours used in refrigeration, radiation and conduction, flow of liquids, vapours, and gases. The chemist or engineer who is called upon to handle gases on a large scale will find in this treatise all that he is likely to require in the way of scientific preparation for his work.

(5) Prof. Sackur's "Text-book of Thermochemistry and Thermodynamics" deals with the fundamental laws of heat and of thermodynamics, which are then applied to many of the chief problems of physical chemistry. Thus we find chapters devoted to the theory of solutions, including van't Hoff's equations for osmotic pressure, and to chemical equilibrium based upon the equations of Helmholtz and of van't Hoff, and applied, for instance, to calculate the heat of ionisation from the change of the ionisation-coefficient with temperature. There are also chapters on the applications of thermodynamics to electrochemistry, thermoelectricity, and capillarity. The chapters deal with radiation and with Nernst's "heat-theorem."

last

(6) The "Foundation Course in Chemistry" of Messrs. Dodgson and Murray is a well-written book of rather exceptional character. Special attention is paid to topics which have an interest for agricultural students, but this is by no means a drawback from the point of view of the general reader, as it gives an air of reality to the whole *reatment of the subject. Structural formulæ are treely used for inorganic as well as for organic compounds, and a long chapter is given up to the chemistry of aliphatic compounds under the title "Paraffins and their Derivatives." The chapter

on general principles gives a clear exposition of the doctrine of equivalents, but is scarcely an adequate exposition of the atomic theory, as Avogadro's hypothesis, which is the real basis of the modern system of atomic weights, is postponed to a later chapter, and is there treated only in the most incidental manner.

(7) The modern system of examinations is responsible for the development of a form of qualitative organic chemistry in which attempts. are made to determine the nature of organic compounds without carrying out a combustion or quantitative analysis of any sort. This type of organic chemistry is only distantly related to the requirements of scientific or technical research, and has only a very limited range of usefulness. But if the student is aware of the supreme necessity of quantitative work there is little harm in allowing him to get some practice in recognising the qualitative properties of the chief radicles. Mr. Shepherd's book gives a scheme whereby the most important groups of organic compounds may be identified by qualitative tests; the scheme has been in use for some years, and has thus been adequately tested by actual work in the laboratory.

OUR BOOKSHELF.

A Text-book of Experimental Metallurgy and Assaying. By A. R. Gower. Pp. xiv + 163. (London: Chapman and Hall, Ltd., 1913.) Price 3s. 6d. net.

THE new edition of this book conforms to the

syllabus of the Lower Examination in practical metallurgy of the Board of Education. The first portion of the book consists of a series of experiments and explanations to illustrate the reactions occurring in various metallurgical operations, while the second part deals, in quite a satisfactory manner, with elementary assaying. It would have been an advantage if the book gave a little more guidance to the beginner, for very often he does

not realise the economic character of metallurgy. For instance, a student sometimes thinks that as sodium carbonate is used in the laboratory as a flux for silica, therefore it would be charged into a blast-furnace smelting copper ores when silica has to be removed. The first chapter of this book may give some students an impression of this kind, for the substances classed as used in metallurgical operations are not all commonly so employed, although frequently used in experimental metallurgy and assaying. Then, again, in the chapter chapter "Formation of Alloys," the theoretical quantities of the metals have been given, and no allowance made for loss in the case of volatile

metals.

During the past twenty-five years the book has proved of use, and the present edition should be of assistance to those preparing for the Board

of Education examination, and if the exercises are performed under the supervision of a teacher, none of its minor defects will cause the beginner to gain wrong impressions.

Ministère de l'Agriculture. Direction Générale des Eaux et Forêts. 2o partie. Eaux et Améliorations Agricoles. Service des Grandes Forces hydrauliques dans la Région des Alpes. Résultats des Etudes et Travaux à la Fin de 1911. Tome v., 1912. Pp. 530.

THE present volume is the fifth of the series published by the French Ministry of Agriculture since the inauguration of the Service of the Great Hydraulic Forces in Alpine regions, and it brings the account of operations down to the end of the year 1911. Of the 530 pages of which the volume consists, 487 are devoted to a tabulation of the results obtained from observations in the basins of the Arve, the Fier, the Isère, and the Drôme. A series of nine charts also accompanies the report, covering the regions of the Arc, the Breda, the Durance, and the Guil.

It is interesting to note the expedients and devices by which an investigation, demanding for its most effective development the employment of expert scientific observers, has been enabled to be carried on to a large extent by voluntary workers and local auxiliaries, for the most part untrained and indifferently coordinated. Such agencies in many cases have had to be relied upon for the collection of data, and as there is a constant change of personality in the assistants, the difficulties in the way of securing trustworthy records are sufficiently obvious.

"However," concludes the prefatory note, "in spite of defects, of which we more than anyone are conscious, we are convinced that the study of hydraulic forces, so far as circumstances permit, constitutes none the less a real utility "—and a cursory glance through the pages of statistical matter, carefully annotated and compiled, bears incontestable witness to the patient labour and exactitude of those engaged in the French hydrographical service and of M. de la Brosse, its chief engineer.

Weather Bound. By R. T. Smith. Pp. 319. (Birmingham: Cornish Bros., Ltd., n.d.)

Price 155. net.

THE author gives, in great detail, summaries of results of twenty-seven years' observations at five stations situated to the west of Birmingham, in a series of tables and diagrams occupying 170 pages. He adds a diary, "Weatherwise and Otherwise,' for the same period, which occupies sixty pages, and explanatory text (seventy-two pages). also gives a diagram of the normal course of the meteorological elements throughout the year, which is unintelligible owing to want of explanation.

The amount of industry displayed is worthy of praise, and most of the tables appear to contain climatic data of real value, but the author's exposition cannot be recommended to the attention of serious students of meteorology.

R. C.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsing opinions expressed by his correspondents. Noti can he undertake to return, or to correspond 2.1 the writers of, rejected manuscripts intended 1 this or any other part of NATURE. No notice taken of anonymous communications.]

Radio-activity and the Age of the Earth.

IN his letter in NATURE of June 26, Dr. Schi quotes with disapproval Mr. Holmes's deduction the "heavy metallic core" of the earth completely destitute of radium"; for this ded. in Dr. Schiller's opinion, "involves the improbabi that the heaviest metal of all, uranium, has not gra tated to the metallic core, and does not expla why this core should be destitute of radio-ar substances."

In the next paragraph, however, Dr. Schiler gests a possible escape from the difficulty with words, it is possible that under the physical cop tions obtaining in the interior uranium does dissociate, or does so much more slowly."

Last autumn, as a sequel to certain speculano |into the effects of pressure on the mineralogical onstitution of the earth's crust at great depths, I a led to a consideration of this very question of t dissociation of elements when subjected to the h temperatures and pressures that prevail at such depth

So far as I was able to discover, no determinati of the specific gravity of radium had then been mar presumably for lack of sufficient material; b judging from its chemical relationship with barig the atomic volume of radium must be much grezithan that of uranium. Heat is known to be evol d during the disintegration of radium, so that the breaup of this element is an exothermic change. I. writing this letter whilst travelling, and am, cons quently, unable to verify my impression that hear is also evolved during the conversion of uranium radium. But in any case, the passage of uran u into radium may be expressed in a general way some such equation as the following:

U=Ra+m+e,

where m indicates the loss of mass due to liberat : of helium in the successive stages of disintegratin and e the loss of energy represented by the vari manifestations of energy. Since radium has a hug atomic volume than uranium we see that the progico of this reaction from left to right means an INICI in volume and an evolution of energy, part of wh is doubtless speedily transformed into heat. In 12: it is exactly the kind of reaction that would be hibited by high pressure and temperature condition. That high pressure should be able to prevent t disintegration of uranium seems reasonable, if n accepts the electronic constitution of the atom. Juding from the extreme length of the half period disintegration of uranium under surface condition. the constituent electrons of an atom of uranium p form on the average a vast number of revoluti before the system arrives at the position of instabil that permits the escape of a helium atom. In f the uranium atom is evidently stable during enormous number of revolutions or vibrations. if, when the electronic system arrives at last at unstable configuration, a sufficiently powerful count balancing force can be applied from without, then system will be helped past the danger point and able to commence another long cycle of movement before the dangerous configuration is again assume In view of the experiments of Humphreys Mohler upon the displacement of the Specir lines, and the work of Richards on the

t

ressibility of elements, amongst other facts, is evidently possible to influence intra-atomic activity by means of forces applied from without. It seems probable, therefore, that pressure, if ficiently great, could be transmitted to the interior ta uranium atom and supply the countervailing force required to help the atom past a position of instability. Once we realise this probability, we see a cogent reason why the interior of the earth should be free from radium and all other radio-active substances the formation of which from heavier elements demands an increase in volume, these heavy elements bring at great depths only potentially radio-active. From this point of view radio-activity is, as Dr. Schiller suggests, "an acquired habit of the substances that exhibit it," the habit being acquired when such an element passes by any means whatever from hat depths below the earth's surface to regions of less pressure.

In a paper just issued in the Records of the GeoJogical Survey of India (vol. xliii., part 1) I have given a preliminary account of these speculations concerning the mineralogical constitution of the earth's crust, and in a final paragraph have appended a brief reference o this question of the inhibition of the disintegration of uranium at great depths below the earth's surface. L. L. FERMOR.

Pianoforte Touch.

I connection with the discussion on this subject originated by Prof. Bryan's paper, I may mention that I have been making some measurements during The past winter with the view of obtaining some idea of the velocities and forces involved in the motion of the transmitting mechanism. By fitting an electric hronographic arrangement to an upright piano I have been able to measure the actual times taken in different stages of the movement with different degrees of loudness.

Among other results, I have found that the time during which the hammer is flying freely towards the string after losing contact with the propelling mechanism varies from about 0.04 sec. for pp to 4001 sec. for ff. The distance of flight was about 1 cm., so the velocity ranged from 25 to 1000 cm. per sec. At the latter extreme, however, the force sed in striking the key was greater than would be used in ordinary playing. On the other hand, when #weight was allowed to fall on the key from the smallest height to produce a note the time could be brought up to 0-07 sec., corresponding to a velocity f only 14 cm. per sec.

With regard to the much disputed point as to whether it is possible to vary the quality of the note independently of the loudness, this must, I think, still be regarded as an open question. Very positive affirmations are made by musicians on both sides. From a physical point of view the suggestion made Mr. Tobias Matthay in his work on touch seems to be the only possible way to explain the effect, if it exists, viz. that the quality can be spoiled by vibraons of the hammer-shaft at the instant of striking the string. In accordance with this, Mr. Matthay holds hat the tone is good when the final velocity is given

the key gradually, and is bad when the same locity is imparted by a sudden blow. That vibraons of the shaft occur is, of course, undoubted, but other they are sufficient to cause an appreciable ut is another matter. On the other side, recent erman theorists, such as Breithaupt, Steinhausen, and Ritschl, deny the effect altogether. The lastmed author holds that good touch consists in the wwer to produce fine gradations of intensity and complete mastery of legato and the use of the „dal,

The essential question seems to be whether good and bad touch can be distinguished in a single note struck and allowed to die away, or in a succession of notes following each other at so long intervals as to be musically detached. As I understand Prof. Bryan, the improvement effected by his invention is chiefly apparent in a sequence of notes forming a melodic phrase. Further, I think that the exact

dynamical effect of the contrivance on the motion of the key has not been made quite clear in the published account. W. B. MORTON. The Queen's University of Belfast, July 2.

The Reflection of X-Rays by Crystals.

this

Ir is interesting to find that an X-ray bulb having a rhodium antikathode gives off a strong, sharply defined (and therefore very homogeneous) beam which is reflected from the (100) face of rock-salt at a glancing angle of 62°. Its mass absorption coefficient in aluminium is 3.2. A second weaker beam is reflected at an angle of 5·8°, and appears to complete the rhodium X-spectrum. Assuming the correctness of my son's determination of the spacing of the atoms of rock-salt (in a paper read before the Royal Society on June 26), the wavelength of the stronger beam is 0.61 x 10-8, and of the weaker 0.57 × 10-8. It can be calculated that radiation of about this wave-length should be emitted by a rhodium antikathode; the argument is given in a paper recently read before the Royal Society (see abstract on p. 496 of this issue).

an

Platinum and rhodium give much stronger homogeneous reflected rays than iridium, tungsten, or nickel. The current produced in ionisation chamber 15 cm. long, filled with SO2, the slits being 3 mm. long and 0.8 mm. wide (Proc. Roy. Soc., lxxxviii., p. 428), is so great that the leaf of a Wilson electroscope races across the field of view at the rate of thirty or forty measurable divisions (three or four scale divisions) in a second. The setting must be exact, and the bulb should be very soft.

W. H. BRAGG.

Rosehurst, Grosvenor Road, Leeds.

Wireless Antennæ.

PROF. FLEMING, in a recent letter to a contemporary journal, has made a suggestion similar to that of Mr. A. Lander, in NATURE of July 3 (p. 451), to the effect that the space wave in wireless telegraphy is supplemented by some effect which travels through the earth. Indeed, it would appear natural to expect that, in addition to the electric disturbance which must travel outwards in all directions over the conducting surface of the earth when the electrical potential at any point on this surface is disturbed, the passage of the electromagnetic waves through the air above the earth's surface should be accompanied by some form of electrical disturbance along the conducting earth's surface beneath them. This is, however, a subject that, so far as I am aware, has not yet been tackled by mathematical physicists, and I would point out that it is well worth their attention.

In connection with the matter, it may be of interest to mention that I find that my own body, without any wires or anything else, will serve as antenna for the reception of signals from the Admiralty. My receiving apparatus is on the ground floor of my house in Chester Square, and with my ordinary aërial disconnected I find I can get the Admiralty signals, faintly but quite audibly, simply by touching with my finger the terminal to which the aërial is usually connected. No doubt in this case my body does not act as an aërial in the ordinary way, but merely as a capacity into which the electrical disturbance arriving

through the earth passes in and out through the receiving apparatus. The Admiralty station is, of course, comparatively near, and the signals are very powerful. This explains why it is only Admiralty signals that I am able to receive by this method.

I am unable to agree with Mr. Lander in his remarks as regards tuning, as I find that with my bedstead aërial it is just as easy to tune in and out such signals as I am able to receive as it is with my proper aërial, which is suspended on poles above the roof of the house. The Eiffel Tower signals are always difficult to tune out, for the reason, as I suppose, that they are of irregular wave-length, while I find it impossible to tune out the Admiralty by reason of its power and proximity. Norddeich and other unidentified signals that I obtain are, however, tuned in and out both with the bedstead aërial and with the other with equal facility.

For time signals very accurately tuned waves, such as are sent out by Norddeich, are perhaps not altogether an advantage, as badly tuned waves, such as are sent out by the Eiffel Tower, are much more easily picked up by all and sundry.

A. A. CAMPBELL SWINTON.

66 Victoria Street, Westminster, S.W., July 7.

A Mechanical Vacuum-Tube Regulator. MAY I supplement Mr. Campbell Swinton's letter in NATURE of June 26? The device of sliding a glass sleeve over the kathode for the purpose of varying the hardness of a discharge tube was also used and fully described by Wehnelt in 1903 (Deutsch. Phys. Gesell. Verh., 5, 14, p. 259), some five years after Mr. Swinton.

The important part that the electrification on the walls plays in a discharge tube is not, I think, generally realised; and Mr. Swinton is not quite right in assuming that Mr. Whiddington's explanation is novel.

The electrification on the glass walls adjoining the

will find it clearly stated that the regulator was c covered by him. RICHARD WHIDDINGIGA

St. John's College, Cambridge, July 7.

The Humphrey Owen Jones Memorial Fund. THE Committee formed to carry out the gerra expressed desire that some suitable memorial of late Humphrey Owen Jones, F.R.S., should be ev.. lished, has received subscriptions amounting to ar 3600l. It is proposed to devote the sum collected the endowment of a teaching post in physical cheristry in the University of Cambridge.

The committee desires to close the subscription, .. at the end of this month, and requests further inten ing subscribers to send their contributions to L account of the H. O. Jones Memorial Fund, Mess Barclay and Co.'s Bank, Cambridge, before that du W. J. POPE

(Chairman of the Committee) The Chemical Laboratory, Cambridge, July 7.

Smithsonian Physical Tables. ATTENTION was directed by Mr. C. T. Whit on p. 320 of NATURE of May 29, to a "very awki error" in the Smithsonian Physical Tables (151 The institution is always glad to have attent directed to errors for correction in subsequent editionbut as this particular error does not appear in first revised, second, third, fourth, and fifth edition it seems rather unfortunate to have discredit threz. on the tables through an error long since corrected C. D. WALCOTT, Secretary. Smithsonian Institution, Washington, U.S.A.. June 21.

MODERN VIEW'S OF ELECTRO-THERA PEUTICS.

kathode rays, were remarked by Goldstein in 1901 (ibid. 3, 15, p. 192).

I remember some half-dozen years ago, Sir J. J. Thomson, in one of his lectures at Cambridge, gave a similar explanation of the formation of the fine pencil of kathode rays which can be seen crossing the bulb from the centre of the kathode in a soft X-ray tube. He attributed the effect entirely to the negative electrification of the glass round the kathode. The pencil of rays is as definite with a plane kathode as with a concave one.

But X-ray tube-makers have long been aware that, by withdrawing the kathode from the bulb into a side tube, the discharge can be hardened. In the earliest X-ray bulbs, the kathode was always mounted in the body of the bulb; but the advantages of a side tube had been realised by 1896, and the design has since been universally adopted.

Mr. Swinton was also responsible about 1897 for another adjustable form of X-ray bulb, in which, instead of a sliding sleeve, a movable kathode could be advanced in or out of a side tube. The bulb is at

the true meaning of the action of electricit upon living subjects have been growing mai clearer. We begin to see the principles up which our practice should be based, and already, as a consequence of this, our methods are changing and our results are growing more valuable.

There are two factors which have brought th about. One is the recognition of the importan of the theory of ions in all matters which concern the movement of electric currents in living tissues, and is due to the genius of Leduc, and the other is the recognition of the thermal action of high frequency currents, an action which remained un appreciated, even if not unknown, until it was insisted on and emphasised by Nagelschmidt. I' is upon these two basic facts, the chemical or ionic effects and the thermal effects of electri currents, that the electro-therapeutics of the future will be established.

In order to remove the possibility of any misunderstanding that may arise from Mr. A. Campbell Swinton's letter in NATURE of June 26 (p. 425), may I state that the mechanical vacuum-tube regulator is not claimed by me as new in the paper referred to. If Mr. Campbell Swinton will read the actual paper he

all movements of current in the body, whether the currents are direct, interrupted or alternating, re ionic movements pure and simple, and their effens are due to the chemical displacements produced We may not speak of effects which are addition to or independent of the ionic movement, for su effects do not exist. The current in the bodys the double ionic movement only. The treatme

electric currents is a chemical treatment, and its hemical actions must explain the results obtained. The stimulation of nerve and muscle is a hemical stimulation by displacement of ions. Nernst, in fact, has expressed the formula for erve excitation in terms of ions. The sensation lt in the skin during the passage of a current a chemical effect, and by altering the composion of the saline solution with which the elecodes are moistened, its character can be altered So that the sensory effects become more noticeble either at the negative or at the positive electrode. With sodium carbonate it is the negative electrode (ions of CO3) which gives the greatest sensation. With sodium chloride it is the positive electrode (sodium ions), and so on in great ■riety. ·

Thus a practical lesson may at once be drawn from a knowledge of ionic effects, namely, that solution of sodium carbonate should not be used for moistening the electrodes in electro-diagnosis, ecause in that procedure a small negative elecErode is used with high concentration of current, and in these circumstances the presence of a carbonate in the liquid causes unnecessary pain to ne patient. Again, in using chlorine ions for the softening of scar-tissue it saves the patient some discomfort and facilitates the toleration of massive currents to use the chloride of ammonium at the anode in preference to that of sodium, because he ammonium ion affects the sensory nerves of the skin in a less degree than the ion of sodium. There is another direction in which the applica- | on of the principles of ionic movement has incased the therapeutic powers of electrical applicaons, and that is in the direction of treatment by rger currents. If we look in the text-books of etro-therapeutics we see continually that rrents of 5 or 10 milliamperes are prescribed. Formerly that was as much as could be given ithout causing discomfort or producing superwial burns. The metal-plate electrodes and the mall buttons or discs covered with a thin layer of chamois leather and set in handles and applied the affected region did not permit the use of rge currents; Leduc has told us why this is the se. With such electrodes the ions of hydrogen and hydroxyl which are formed at the metallic urfaces can quickly reach the skin surface.

They ire strongly caustic and tend to produce pain ind burns, and this can be obviated by the use of electrodes composed of thick, folded cloths wer which is laid a metal electrode faced with o or three layers of thick felt. The whole is noistened with appropriate saline solutions and andaged to the patient, who thus can tolerate pplications of 50 milliamperes or more, and that or times of fifteen or twenty minutes or longer ithout any burning or blistering of the skin.

ment of paralysed muscles. A distinguished French writer has recently told us that he has gradually increased the duration of his electrical applications in such conditions to periods of one hour twice daily, and uses rhythmic currents which are not less than 25 milliamperes, and that in the infantile paralysis of children the little patient is so slightly inconvenienced by these applications as to play and even to sleep while they are proceeding; also that the results of such intensive treatment are entirely good, and produce not the least sign of fatigue or exhaustion.

The ionic theory of electrical treatment which has shown us how to use large currents has also shown the necessity for them. If the results to be gained are produced by the chemical interchange set up in a tissue, it is manifest that to obtain them one must use a strength of current which is capable of producing a distinct effect; and for the same reason the time of an application must be lengthened. The chemical changes caused by a current of 50 milliamperes for twenty minutes are ten times greater than those given by 10 milliamperes for ten minutes, and are therefore ten times more likely to produce an appreciable effect. appreciable effect. The results of adopting this view and of increasing the quantity of current employed may make all the difference between success and failure. It is thus that the treatment of neuralgias can be made effective, and the same occurs in the treatment of many affections of the joint structures.

In the ionic theory of electrical treatment we have to consider two factors the chemical interchanges set up within the tissues and the introduction of ions from without. The second of these considerations has added notably to the scope of electrical treatment. In the treatment of superficial morbid states there can be no doubt of the actual penetration of the external ions into the part treated; and the use of the zinc ion introduced at the positive pole from material moistened with a solution of a zinc salt has led to the successful treatment by electrical means of a whole series of superficial ulcerative conditions of the skin and the various orifices of the body.

In the treatment of affections of the deeper tissues the method of the introduction of ions from pads moistened with appropriate solutions has also achieved many successes, notably in conditions of so-called neuralgia, states which are almost always due to neuritis or perineuritis-for example, in many severe neuralgias of the trigeminal nerve. Quinine and salicylic acid, the latter especially, are useful in these conditions when introduced by the electric current.

In chronic gouty conditions the introduction of the salicylic ion is also of great value. Iodine ions and lithium ions to a lesser extent also seem to be useful in gouty conditions. The chlorine ion, recommended by Leduc for its softening action upon scar-tissue, has proved itself valuable. Leaving the chemical effects of electrical currents, let us turn to the consideration of the