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LETTERS TO THE EDITOR.

and questions of this kind can only be settled by the

decision of many eyes, and their decision only applies (The Editor does not hold himself responsible for

to themselves.

JOHN AITKEN. opinions expressed by his correspondents. Neither

Ardenlea, Falkirk, August 10. can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for “The History of Upper Assam, Upper Burmah, and this or any other part of NATURE. No notice is

North-Eastern Frontier." taken of cnonymous communications.)

I have had the opportunity of looking through this

recent publication, which was reviewed in NATURE, Colour Sensation.

vol. cxiv., p. 481, December 31, 1914. It is most IN NATURE of July 15 there is given an abstract of interesting reading to anyone, but particularly to a paper by Dr. F. W. Edridge-Green in which he

those like myself who spent many years on the gives reasons for supposing that the sensation pro

Eastern Frontier among the tribes mentioned. This duced by spectral yellow is a simple sensation, and

book covers so large an area, goes back so far into not a compound of red and green, as supposed by

the past history of Assam since the East India Comthe Young-Helmholtz theory. In 1872 I read a paper

pany were brought into relation with that country, on colour sensation before the Royal Scottish Society and further back into a lost history of its ancient of Arts, in which practically all the experiments greatness, that 256 pages cannot do the subject described by Dr. Edridge-Green are given, but the justice. Very much which has been written of conclusion come to was that spectral yellow gave a

Assam, particularly in the Journal of the Asiatic compound sensation, because it could be altered by Society of Bengal and other publications, is not refatiguing the eye with either red or green. I have

ferred to at all, while certain parts very látely repeated these tests, and find my eyes still give sketchy, even inaccurate. At the same time, very the same reactions. To my eyes, the best yellow

much that Colonel Shakespear has written is exis just on the green side of the D lines in the spec

tremely interesting, and his knowledge and experitrum, but if the eye is fatigued with red light the ence are very considerable, from having served so long yellow is changed to greenish-yellow, and if fatigued in the country, and his conclusions sound. On p. with green it is changed to orange, that is, the 108, treating of events in the Dafla country in 1874, yellow changes in colour towards the unfatigued when Colonel Stafford commanded a force which sensation. Testing by means of a sodium fame

entered the country, we find :gives the same result. In making this test, the flame

“The Daflas made no resistance, but paid up fines should not be used immediately after lighting it, as

and returned the captives. Little or nothing was it then contains, in addition to the bright yellow

done by this large force in exploration or survey, lines, a continuous spectrum. The test should be

and it returned to Assam amidst a clamour from made when the flame is nearly burnt out and the

Government over wasted money" (the words in italics salt crackling In that condition only the yellow

are mine. I would answer this statement by the lines are visible, and it shows the change better than following extracts from Reports, etc.). in its first condition. To the eye fatigued with red I. The Indian Museum, 1814-1914. Calcutta, 1914. it has a distinct greenish hue, while to the other eye “ Bhutan is still an unknown country to naturalists, fatigued with green it is reddish. The change is and its territory represents the most important gap in quite marked, and there is no hesitation as to the our geographical knowledge of the Himalayan fauna. conclusion.

East of Bhutan two expeditions of very different date With regard to the results given in the abstract are of zoological importance, namely, the Dafla exof Dr. Edridge-Green's paper : (1) Fatiguing the pedition of "1874-75' and the Abor expedition of eyes with pure yellow spectral light could hardly be 1911-12. On the first of these, Godwin-Austen, then expected to affect the hue of the red, and could only a Major in the Bengal Staff Corps attached to the slightly diminish its brightness, which will be diffi- Survey of India, himself made collections of great cult to detect. (2) It is difficult or impossible to com- value, and also encouraged his subordinate officers pare results when the eye in one case is flooded all to do the like." over with a bright light, and the other in which it II. As to the survey work. In a Memoir on the is fatigued with a narrow strip of weaker light Indian Surveys, by Člements R. Markham, C.B., which cannot be kept on the same part of the retina F.R.S. India Office Publication. 1878, p. 173., for any length of time. Results (3) and (4): Dr. “In 1875 Major Godwin-Austen accompanied the Edridge-Green's eyes and mine do not give the same Duftla military expedition against the tribes on the results as stated at the beginning of this letter. northern frontier of Assam. Narainpur, on the Dik

It may be stated that the after-image seen on a rung Nullah, was reached on December 2, 1874, and white surface after looking at spectral yellow, and from a base on the banks of the Bramaputra a by the sodium flame, is the same as that given by a short series of triangles was extended northward into yellow compounded of red and green. Now if the Duffa hills. Owing to the brief period during spectral yellow gave a simple sensation we would which the military were in the country, the survey hardly expect this, as the after-image is a compound party were unable to remain beyond two and a half of all the unfatigued sensations, and we would expect months. The out-turn of work amounted to 1705 spectral yellow if simple ought to give a nearly white square miles of entirely new topography, on the scales after-image, and not a violet one.

of two and four of the season's work in the Duffla There is an old saying that “Seeing's believing." hills, has been compiled by Major Godwin-Austen, In ordinary matters this may be so, but the belief is and is a valuable addition to our geographical know. not necessarily true, and in questions of colour full ledge of the region beyond the northern frontier of of pitfalls. No two pairs of eyes see colours alike. Assam. Lieut. Harman, R.E., rendered assistance This does not refer to colour-seeing and colour-blind by surveying the course of the Ranga river; and Mr. eyes only, but there is reason to believe that all Lister, of the Royal Botanical Gardens, Calcutta, eyes differ more or less in their perception of colour, was assiduous in making a collection of plants, seeds, and dried botanical specimens. The Surveyor

THE GAS INDUSTRY AND EXPLOSIVES. General expresses a hope that these explorations on the Northern Assam frontier will be continued and THE need that has arisen for certain coal-tar

, is of tact all difficul

by of ties in the way of visiting and exploring the narrow the high explosives essential in the present war, has strip of hills between the Assam valley and Tibet may riveted attention on the best methods for obtainbe overcome." As to the natural history work, there was pub-ing these, and of keeping up the supply to the

highest possible amount during the period of lished :III. Journal Asiatic Society of Bengal, vol. xliv.,

hostilities. part ii., 1875: Notes on the Geology of part of the

The substances most needed are the aromatic Dafla Hills, Assam; lately visited by the Force under hydrocarbons, of which benzene forms the base Brigadier-General Stafford, C.B., by Major H. H. from which the newest and most powerful of these Godwin-Austen, F.R.G.S. F.z.s., etc., Deputy explosives, tetranitroaniline, is prepared, and also

, Superintendent Topographical Survey of India, with the tetranitromethylaniline, which under the name map. Plate ix.

of “tetryl” is playing an important part in detonaIV. Journal Asiatic Society of Bengal, vol. xlv.,

tors and primers. Toluene, the next member of part ii., 1876: On the Helicidæ collected during the Expedition into the Dafla Hills, Assam, with

the aromatic group, is needed in enormous quantiplate viii., p. 311.

ties to nitrate to trinitrotoluene, or T.N.T., whilst V. On the Cyclostomacea of the Dafla Hills, Assam, carbolic acid is the base from which picric acid p. 171, with plates vii. and viïi. a.

is formed, this body under slightly varying condiVI. List of the Birds collected on the Expedition into tions being the English explosive lyddite, the the Dafla Hills, Assam, together with those obtained

French melinite, and the Japanese shimose powder. in the adjacent Darrang Terai, with plates iii. and iv., p. 64, by same author.

The aromatic hydrocarbons found in the coal-tar H. H. GODWIN-AUSTEN.

are only a small proportion of those existing in the gas, as the volatility of the so-called benzols—

benzene, toluene, and xylene—causes the largest Moustier Implements and Human Bones in Suffolk.

proportion of them to be carried forward as

vapour in the coal gas, and on cooling this gas Owing to the liberality of the trustees of the Percy Sladen Memorial Fund, I have been enabled during

and scrubbing it with creosote oil a much larger the past eighteen months to conduct a continuous

yield is obtained from the gas than from the tar. series of excavations in the south-west corner of

The formation of these bodies is due to the action Messrs. Bolton and Laughlin's brickfield, Ipswich,

of heat on the primary constituents of the decomwhere a well-marked “occupation-level" occurs rest

position of the coal, and when coal is distilled at ing upon a weathered surface of chalky boulder clay, very low temperatures the primary products of and covered by a very hard and compact sandy loam the decomposition, which largely partake of the of . It bifrea gravish colour it appears that since the people character of paraffins, i.e. saturated hydro

, lived who occupied this

, now dry, has been deepened considerably, and as

foundwhilst the aromatic the “floor " passes into a small escarpment to the

carbons are to all intents and purposes absent. south at a depth of about 10 to 12 ft. from the surface

As the temperature of carbonisation is raised, the of the ground, it seems that a considerable antiquity

paraffin hydrocarbons become less in quantity, must be assigned to the human relics associated and naphthenes make their appearance in the tar. with it. The occupation-level under investigation is At still higher temperatures, these naphthenes very rich in flint implements, which, in my opinion, split off hydrogen and become converted into must be assigned to the Moustier epoch. (Traces of aromatic hydrocarbons, such naphthenes as another occupation-level occur above the Moustier

hexahydrobenzene being converted into benzene deposit, containing implements of a totally different

with evolution of hydrogen. As the temperature type which approximate to the earlier Aurignac

. examples.) With the flints have been found several

of carbonisation is still further increased, the hundreds of animal bones, representing chiefly the

tendency is for these bodies to become converted remains of the horse, and one specimen referable to into naphthalene, whilst the employment of very the mammoth. Numerous fragments of very rough high temperatures with light charges gives rise to and primitive pottery occur in the floor, and tend a tar which contains only very small traces of to support Dr. Rutot's claim that about five hundred

aromatic hydrocarbons, large quantities of naphfragments of pottery were found at Caillou-qui-Bique, thalene, and a very large proportion of free associated with upper Le Moustier industry. Three portions of the human skeleton have been found

carbon, produced by the degradation by heat of scattered upon the “floor” with the flints and mam

the other hydrocarbons present. malian bones. These comprise a small portion of the

When, however, vertical retorts and heavy upper margin of the occipital bone of a skull 10 mm. charges with horizontal retorts were introduced, in thickness, the shaft of the left humerus of a a marked improvement in the quality of the tar woman, and the shaft of the right femur of a man. took place : the heat from the walls of the retort There seems little doubt that any of the bones found

passing slowly into the mass of coal distilled off belonged to individuals of the Neanderthal race. All the human and animal bones are well preserved and

the tar vapours at the lowest possible temperain a condition of fossilisation. The excavations are

ture, and these, finding an exit through the comstill in progress, and it is hoped that further dis- paratively cool core of the coal to the mouthpiece, coveries will be made.

J. Reid Moir. a large proportion of the lowest temperature tar 12 St. Edmund's Road, Ipswich, August 13. was produced. As the charge became more and

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more thoroughly carbonised, the central core THE ELECTRONIC THEORIES OF THE became blocked with pitch and tar distilled for

PROPERTIES OF METALS. ward into the coal mass, and the gas and tar vapour being in this latter stage forced to find

N a course of lectures delivered at the Caventheir way through the outer shell of red-hot coke,

dish Laboratory during the Michaelmas term became degraded to the utmost limit, and gave result of assuming the passage of electricity

of 1886, Sir J. J. Thomson examined the dynamical very large volumes of such permanent gases as hydrogen mingled with methane, the least easily through a metal to be of the same nature as broken up of the hydrocarbons,' the result being through an electrolyte. The subject was dealt

with that the modern tar is in reality a mixture of low

more completely in “Applications of temperature and very high temperature tar.

Dynamics to Physics and Chemistry" in 1888. Such a tar, obtained from a good gas coal, will

The later discovery of the electron which might contain approximately :--

act as a carrier of electricity from molecule to

molecule placed the idea on a much firmer footing, Benzol

0*60 per cent. and in 1898 Riecke developed theories of the elecToluene

0 15

trical and thermal conduction and thermo-electrical Solvent naphtha

properties of metals, based on the existence beHeavy naphtha

1.65

tween the molecules of carriers of positive and Carbolic acid

0-6

negative electricity. Two years later Drude Cresylic acid

0'9

worked out more systematically theories founded Creosote oil

30-6

on the same basis, and it is his work which is The remainder is naphthalene, anthracene, and usually quoted in accounts of electronic theories, pitch.

generally with the simplification that only one If the gas from the carbonisation be scrubbed, type of carrier—the negative electron—is taken as and the absorbed hydrocarbons be distilled out

moving freely between the molecules. These from the creosote oil and added to the light hydro- electrons are supposed to be produced by the discarbons obtained from the tar, the total yield is :- sociation of the electrically neutral metal atoms,

what remains of the atom being left positively Benzol ...

2.1 per cent. charged. Toluene

The moving electrons are assumed to have the Solvent naphtha

2.6

same average kinetic energy as a molecule of a Heavy naphtha

2:6

gas enclosed in a cavity in the metal would have. It is found in practice that the carbonisation

The nature of the impact of electron on metal under the ordinary gasworks conditions of a ton

atoms is not discussed, but as the motion of each of good bituminous coal yields about one-third

metal atom is likely to be comparatively small, of a gallon of toluene from tar and gas.

the gas laws which hold for the motions of the In practice, the withdrawal from the gas of all

molecules of a light gas amongst those of a much the hydrocarbons that can be scrubbed out by have a mean free path of length 1.

heavier are applied and the electrons are said to

The motions creosote oil would reduce the heating value of the gas to a considerable extent, and various methods

are distributed in all directions equally, and the of getting over this trouble have been proposed, metal unless their speed perpendicular to the sur

electrons cannot escape through the surface of the such as enriching the scrubbed gas by the benzené metal unless their speed perpendicular to the surand xylene from the crude benzol, after separation violet light on the surface facilitates the emission.

face exceeds a certain limit. The action of ultra. of the toluene by fractional distillation, or by so scrubbing the original gas that only about one

When an electromotive force is applied to the third of the crude benzol is withdrawn, as by

metal there is superposed on this to and fro motion such means the calorific value of the gas ca be

of the electrons a drift up the electric field, the maintained at or above the statutory minimum of

relation of which to the field is such that the 500 British thermal units.

specific conductivity of the metal is proportional The tar and gas made in small country works

to na / NT where n is the number of free electrons as a rule contain more aromatic hydrocarbons per cubic centimetre and T is the absolute temthan the products from large works, as the tem- perature of the metal. Since the electrical conperatures used in carbonisation are not so high; ductivity of a pure metal is known to vary and should the Government need still larger approximately inversely as the absolute temperaquantities of toluene and carbolic acid for nitra- ture, this implies that na must vary inversely as tion, the gasworks of the Empire could treble VT. As there is nothing on the one hand to the output by reverting to the temperature and suggest so considerable a change of the free space

a methods employed before the introduction of re- between the metal atoms with temperature, while generation in the furnaces. This, however, would on the other the facts of thermoelectricity are reduce the gas yield from the 13,000 cubic feet against any considerable decrease in the number per ton now aimed at by the gas manager to of electrons per c.c. as the temperature rises, it 10,000 cubic feet, but the higher calorific value sems difficult to reconcile the law of variation of of the gas would allow of the volume being made nd with experimental facts. up by the addition of blue water gas.

If a slope of temperature exists in a metal, the electrons coming from the hotter side of a cavity postulates is so great that an increase of 1° C. in between two metal atoms will move more rapidly their mean temperature involves a supply of heat than when coming from the colder. There will ten times the specific heat of the metal. After therefore be a drift of energy towards the colder pointing this out Sir J. J. Thomson, in 1907, in his metal which bears to the slope of temperature such Corpuscular Theory of Matter," developed a a relation that the heat conductivity of the metal new theory which may be called the doublet is proportional to navT. As the heat conductivity theory. According to this theory the atoms of a of a pure metal changes very little with change metal are grouped together in pairs, one of each of temperature, this equation again implies that pair positively, the other negatively charged. In na varies inversely as ✓T, and we have the same

ordinary circumstances the axes of these doublets difficulty in understanding how this is brought point in all directions on the average equally. about. On dividing the heat conductivity by T

Under the action of an electric field the doublets times the electrical conductivity the product na tend to arrange themselves in lines, with the disappears from the result, and we obtain a con

positive end of one near the negative of the next stant the value of which should be approximately and electrons may pass from the negative end of 2'3 x 108 for all metals at all temperatures. At

one doublet to the positive of the next, and so air temperatures the values found experimentally along the line of doublets. vary between 2 and 3 x 108, and at very low tem- On the assumption that the axis of the doublets peratures between 15 and 3 x 108. The agree- distribute themselves according to the gas law, ment between the two results is undoubtedly good,

that their centres are · spaced on the average b but when the calculations are improved in accuracy

apart while the charges of the same doublet are by taking into account the variation of the speeds d apart, and p electrons are discharged from a of the electrons about the mean value used by doublet per second, the electrical conductivity of Drude, Lorentz finds the constant 1'5 x 108, which

the medium works out proportional to nbdp/T is not in such close agreement with experiment.

where n is the number of doublets per c.c. and T For alloys and conducting salts the experimental the absolute temperature.

the absolute temperature. The experimental facts values are considerably higher than for pure

show that nbdp is independent of temperature. metals, and Koenigsberger and others have put in the same way the transport of kinetic energy this down to the part played by the atoms them- by an electron leaving a doublet at a higher, and selves in the conduction of heat. For quartz and joining one at a lower temperature, leads to a other electrical insulators which are good con- heat conductivity proportional to nbạp, which the ductors of heat there can be no question of the in- experimental facts show is independent of temsignificance of the role of the free electrons. perature. The quotient of the heat conductivity

Owing to the different values of the concen- by T times the electrical conductivity on this tration n of electrons in different metals, there theory comes 2'6b/d x 108, and as b/d must be will be a flow of electrons through the surface of greater than unity the agreement with the expericontact of two metals till the potential difference mental value 2 to 3 x 108, is about as good as in produced stops the flow. In an unequally heated the case of the simple theory. The presence of metal the same process of compensation will the b/d makes it possible to include in the theory occur. In the former case we get the Peltier and those substances for which the quotient is high. in the latter the Kelvin effect. The former agrees

At the junction of two metals the excess flow in order of magnitude with the values found by from one metal will cause a difference of potential experiment, but as Sir J. J. Thomson has pointed and an electric field which will change the orientaout, it is difficult to reconcile the great decrease tion of the doublets until the flows are equalised. of electrical conductivity of a metal on melting in an unequally heated metal the same method of with the small Peltier effect between solid and compensation will come into play, and we have molten metal. The calculated Kelvin effect shows the Peltier and Kelvin effects. that the concentration n of the electrons must in If the rotation of a doublet in an electric field all metals be nearly proportional to VT, a result does not take place about the middle point, the which is not easily reconciled with that for na two charges of the doublet move with different deduced from the electrical

thermal

speeds. If they are in a magnetic field its action ductivity.

on them will tend to incline the axis of the doublet Since a negative electron in motion in a mag

to the plane containing the two fields, and there netic field is acted on by a force transverse to its

will be a flow of electrons at right angles to both path, the theory affords a simple explanation of

fields. The direction of the flow will be deterthe Hall effect, and gives the right sign and mined by that of the end of the doublet which order of magnitude for the effect in bismuth at moves most quickly. We thus have an explanaordinary temperatures, but the wrong sign for

tion of the Hall effect, whether it be positive or the effect at low temperatures, and for the effects negative. at ordinary temperatures in iron and antimony. No numerical comparisons of theory with ex

In no field can the simple electron theory be periment appear to have been made in the case of said to have given a satisfactory quantitative these thermo-electric and thermo-magnetic effects. account of the facts, and its elaboration in one In his addresses to the Institute of Metals on region has in general led to greater difficulties in May 5, and to the Physical Society on June 25, others. The kinetic energy of the electrons it Sir J. J. Thomson dealt with the modification of

or

con

his theory necessary to bring it into line with alkaline and becomes actively bactericidal. Such the discovery by Prof. Kamerlingh Onnes that at a water would, however, be unfit for domestic and very low temperatures—4° or 5° absolute—the trade use, but if the excess of lime present be electrical conductivities of metals become infinite. removed by the addition of a sufficiency of water The external electric field applied to the metal is from which the bacteria have been removed, the assisted in bringing the axes of the doublets into whole of the mixed water will be softened and line by the field produced by those doublets already purified, and will be satisfactory for all purposes. in line. The kinetic energy of thermal motion of Dr. Houston has previously shown that if raw the doublets tends to destroy the alignment. At river water be stored for from four to five weeks ordinary temperatures it is sufficient to destroy the the great majority of the bacteria are removed, and alignment so soon as the external field is with the water is rendered safe for drinking purposes. drawn, and the flow of electrons from doublet to The excess lime method of purification consists, doublet is stopped. But at very low temperatures then, in the addition of an excess of lime, storage the energy is not sufficient to modify an alignment of the alkaline water for a day or thereabouts, once produced, and the flow of electrons con- so that the bactericidal action may be exerted, tinues when the external field is withdrawn. The addition of a sufficiency of water, purified by conductivity in these circumstances will be very storage, to neutralise the excessive alkalinity, and high.

filtration to remove the precipitated carbonate of · From this short account of the present position lime. of the two theories it will be seen that the doublet Dr. Houston has tested the method on a large theory of Sir J. J. Thomson has shown a greater scale at Sunbury and at Aberdeen. At Aberdeen power than the electron theory of co-ordinating Bacillus coli (which may be taken as an index of the facts of experiment. It has difficulties of its pollution) was present in the untreated water in own, both in the nature of its fundamental from 1 c.c. to 100 c.c.; after treatment it was not assumptions and in its power of reproducing the found in 100 c.c.; the process is therefore efficient facts quantitatively. It does not appear to pro

It does not appear to pro- and it is comparatively inexpensive. vide electrons for emission by incandescent Another research which has been carried out by bodies, and in its latest development it involves Dr.

Dr. Houston is an investigation of "water serious changes not previously suspected in the microbes ” giving the cholera-red reaction after thermal, thermomagnetic, and thermogalvanic incubation of cultures for twenty-four hours. The properties of metals at the very low temperatures cholera-red reaction (obtained by adding acid to attained by Prof. Kamerlingh Onnes. But the a culture) is a very constant and characteristic great flexibility it has shown justifies a more reaction of the cholera microbe, and as this generous treatment of it by those authors and organism is frequently conveyed by water, it is lecturers who have been content to limit their ex- important to know whether water organisms other position of these questions to the older electron than cholera yield the reaction. It is satisfactory theory.

C. H. Lees.

to find that, although eighty microbes out of

approximately 1885 sub-cultures gave the choleraTHE STERILISATION OF WATER.

red reaction on first being tested, they were easily HE safeguarding of our water supplies is of distinguished from cholera by the application of

two or three further simple tests. particular importance at the present time,

Dr. Houston is to be congratulated on the for there may be considerable risk of pollution

valuable research work he has been able to carry if typhoid and cholera cases or “carriers” arrive

out in the midst of a vast amount of routine work. in any number from the seats of war, as may

R. T. HEWLETT. well be the case. The research work carried out by Dr. Houston is therefore of much value and is summarised in a Report just issued. 1

THE LATE PROF. J. COOK Wilson. Dr. Houston first deals with his excess lime"

DEATH has of late been busy among Oxford method of purification. The hardness of water is

Cook chiefly due to bicarbonate of lime (temporary) and Wilson, Wykeham Professor of Logic, was not sulphate of lime (permanent), the former being unexpected,' for he had been in bad health for

, kept in solution by the carbonic acid present. In more than a year, and indeed had never recovered the softening of water lime is added and combines

completely from the shock of his wife's death in with the free and semi-combined carbonic acid, January, 1914. Cook Wilson was a man of quite causing a precipitation of the lime added and of exceptional attainments. Born at Nottingham the bicarbonate of lime in the water in the form

and educated at Derby School, he matriculated at of the relatively insoluble carbonate of lime. A Oxford in 1868. As scholar of Balliol he took no water treated with the right amount of lime has fewer than four first classes, two being for matheno caustic alkalinity and has practically no action matics and two for classics. These were followed on the bacteria present. When more than enough by the Latin Essay, the Conington Prize, and a lime is added the water is rendered caustically fellowship at Oriel.

fellowship at Oriel. After his election as Wykei Metropolitan Water Board. Eleventh Report on Research Work,

ham Professor he became a fellow of New Coltogether with Index to Research Reports, Nos. i-x inclusive. By Dr. A. C. lege, but his affection for Oriel never waned, and Houston. Pp. vii +52. (London: Metropolitan Water Board, n.d.)

his connection with his old college was of late

THE

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