LETTERS TO THE EDITOR.

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

Fine Chemicals for Research Purposes.

IN view of the shortage of fine chemicals which are used for research purposes, we thought it advisable to issue a circular to the principal laboratories in the kingdom asking for lists of chemicals not in immediate use, so that it would be possible to put the holders of such chemicals in touch with those chemists who were in urgent need of them. The replies which have been received so far have been in most cases to the effect that the holders wish to keep their own stocks in hand, but are willing to use our bureau for the purpose of purchasing others. As this attitude is one which entirely defeats the object with which the inquiry was started, may we direct the attention of chemists to the fact that it is impossible for them all to hold and to purchase at the same time. An equitable series of exchanges is all that can be arranged at the present time; and it should be remembered that even 50 grams of some particular substance may make all the difference between the carrying on or the hanging up of a piece of research work.

H. B. BAKER. J. F. THORPE. M. A. WHITELEY. The Imperial College of Science and Technology, South Kensington.

A Penalty on Research.

I AM sure that the biologists of the country will support Sir Wm. Ramsay's protest in NATURE of February 11, on the penalties incurred by men of science for the use of alcohol in their investigations. A few years ago I received a consignment of specimens of natural history in alcohol from a foreign Government expedition for scientific study and description. After some correspondence with the Customs House authorities I was allowed as a concession either to pay the full duty on the alcohol, or, in the presence of an officer, to pour it down the sink in the University laboratory, and replace it by methylated spirit at my own expense. Comment is unnecessary. SYDNEY J. HICKSON.

The University of Manchester.

The Prices of Chemicals.

A WELL-KNOWN firm of dealers in chemicals and laboratory apparatus gave a quotation some days ago for the supply of an ounce each of dulcite and adonite. They proposed to charge gl. 1os. for the former and 61. for the latter. In the price list of chemicals issued by the same firm some months before the war the prices were respectively 45s. and 18s. Is there any good reason (except greed) for this increase of price? Presumably this firm, or some other English firm with which they deal have held a stock of these sugars since before the war. The substances are indispensable in public health bacteriological work, and is it not possible that some university laboratory can undertake their preparation and distribution at cost price? J. J.

The University, Liverpool, February 3.

Oz.

WE are in receipt of your letter of February 8 We with regard to the price of dulcite and adonite. very much regret that your correspondent has not gone more fully into the matter before making charges against firms who are trying to help British industries at a critical time. We should welcome a visit from your correspondent as he may not know the difficulties which have been experienced in obtaining the raw material for the manufacture of dulcite. Dulcite originally was a by-product, and was sold at 4s. 6d. per The price before the war rose in stages from 4s. 6d. to 15s., then to 25s., then to 355., and finally to 45s. per oz., which was the price ruling on August 1. We had at that time only a small stock of both dulcite and adonite consisting of about 8 oz. We purchased a further supply of both these chemicals on or about August 18, but at considerably advanced prices, the supplies being obtained from wholesale chemical merchants in this country. We thereupon raised our prices to 100s. per oz. in the case of dulcite and 36s. per oz. for adonite; this gave us the same rate of profit as we had obtained from dulcite and adonite before the war.

This supply lasted us until December, when we were able to obtain a very small quantity of these two chemicals from small laboratories who had gone to the expense of manufacturing, and the prices being considerably advanced, necessitated the selling prices being raised accordingly.

At the present moment we have no dulcite of any description in stock, and have not had for some weeks. The total amount which we had for sale at a higher price did not exceed two ounces.

oz.,

We have made arrangements with a firm of chemical manufacturers to manufacture for us dulcite and adonite at a price which will allow us to revert to the prices ruling between August and December last. but although delivery has been promised us several times we have not yet received delivery of even and we shall be only too pleased to buy any quantity of dulcite and adonite at the present moment, irrespective of price; our main point is to be able to supply chemicals which are urgently needed, and not to obtain exorbitant profits, and in the case of these two chemicals we may state we have been to considerable expense in endeavouring to obtain the necessary raw material for the manufacture of dulcite and adonite. A FIRM OF DEALERS IN CHEMICALS. February 9.

British Supplies of Laboratory Ware.

As chairman of the British Laboratory Ware Association I have had my attention directed to a circular letter issued by the British Science Guild, dated January, 1915, to schools, colleges, universities, and technical institutes, and also to circular No. 885 issued by the Board of Education, dated January 11, 1915, and which I note is referred to in NATURE, page 580, January 21, 1915.

These circulars have been issued under a grave misapprehension, and are likely to give a very misleading idea of the present situation in reference to supplies of laboratory glassware, and I think that it is very important that any anxiety on behalf of the readers of NATURE should be immediately allayed. I therefore beg to place before you the following information :

The British Laboratory Ware Association, which consists of about 75 per cent. of the apparatus supply firms in the United Kingdom, was formed a few days after the outbreak of the war, in order to co-operate i in connection with the production in this country of

laboratory glassware, porcelain filter papers, etc., not hitherto produced in this country.

The association is not a ring or financial combine, but is merely arranged for the pooling of information and for saving as much time, and preventing as far as possible duplication of correspondence with works, in the way of inquiries and information; the standardisation of sizes for moulds where works undertake to make; and the elimination of difficulties which would occur if all the various firms were working independently.

So far, after months of correspondence, interviews, conferences, meetings, and considerable expense, the association has solved the problem in connection with glass ware, and in a few weeks' time the various firms constituting the association will be in a position to supply the most useful sizes of glass beakers and flasks in an English-made glass similar to Jena glass, which has been tested by well-known English men of science, and can be definitely and safely recommended.

The same holds good for porcelain evaporating basins, beakers, crucibles, and covers, etc., and also for an English-made filter paper equal to the German quality of Schleicher and Schull No. 595, and further qualities of these filter papers will be forthcoming very shortly. Also, as time goes on, further items will be added to the list, as negotiations are brought to a successful issue.

You will therefore see that a great deal of important and valuable work has been done, and that the problem of glassware has been to a very great extent solved so that an English-made glass equal to the well-known Jena glass will be on the market and can be supplied in a few weeks from the present time by the various firms constituting the British Laboratory Ware Association.

C. A. MERCER,

Chairman of the British Laboratory Ware Association, Ltd. 34 Camomile Street, E.C., London, February 8.

be found to be consistent with quantitative measurements of the energies of the two secondary radiations, but are the only rational conclusions which can be drawn from experiments on some substances. The deviations which have been observed in other cases are subjects for further investigation; the nature of these will be indicated later.

These conclusions may be described in greater detail as follows::

If a primary Röntgen radiation of wave-length μ, fall upon an element with a characteristic radiation of wave-length 2, then provided μ, is less than μ, the primary radiation is specially absorbed, and the element emits the particular fluorescent X-radiation, together with an associated corpuscular radiation. If we denote the energy of the primary specially absorbed in connection with the emission of the fluorescent radiation (of Series K, say) by Ek, the energy of the associated corpuscular and fluorescent radiations by C and F respectively, then Ex=CK + FK. Also as the energy of each electron in the corpuscular radiation is approximately (possibly accurately) that of a quantum of the primary radiation (we make the usual assumption here, that there is only one velocity of ejection; good reason can, however, be given for this):

:

FK energy of fluorescent radiation

Ск

=

Problems of Radiation.

THE study of the production of homogeneous Röntgen radiation reveals some of the most interesting and suggestive facts bearing upon the problems of radiation. A few of these will be briefly indicated.

The emission of a fluorescent X-radiation by an element exposed to a primary X-radiation of shorter wave-length necessitates the absorption of a greater amount of energy from the exciting primary beam. It is possible definitely to assign a given portion of the energy absorbed from the primary beam as connected with the emission of a particular fluorescent radiation (Barkla and Sadler, Phil. Mag., 1909.) The element exposed to this primary radiation emits also a corpuscular radiation, a portion of which is definitely associated with each fluorescent X-radiation. measurements of these associated quantities, certain broad conclusions have been found to hold at least approximately in all cases hitherto dealt with; they hold within the limits of experimental error in the one case carefully investigated. These are:

From

(1) The number of quanta of fluorescent X-radiation emitted is equal to the number of high-speed electrons in the corpuscular radiation (the associated corpuscular radiation).

(2) The total energy in the corpuscular and fluorescent radiations is equal to that of the primary beam absorbed.

These are not merely hypotheses which by trial may

bromine the one on which the most trustworthy data have been obtained. Instead of the fluorescent radiation in the particular case carrying away 50 per cent. of the energy of the primary radiation specially absorbed, experiments indicate about 47 per cent. and approximately an equal value for the corpuscular radiation. But there is evidence that with elements of higher atomic weight a limiting value of about 50 per cent. would be obtained. The indication of such a limit gives strong support to the whole theory. On the other hand, from an element of low atomic weight, the experimental value for the fluorescent radiation comes below 30 per cent., and there are indications of even lower values.

It would, however, be remarkable if such a simple theory gave perfect agreement for all elements, and correspondingly all X-radiations. The facts indicated appear of fundamental importance; deviations-real or apparent-will receive investigation and discussion later.

Other important conclusions based on the investigation are that the absorption by an atom is not necessarily in whole quanta of the primary radiation; we have evidence of absorption of primary radiation in quantities of any magnitude between one and two quanta of the primary radiation, or just possibly in fractions of one quantum.

The transformation of primary radiation into fluorescent radiation in certain cases at least is accompanied by little, if any, appreciable loss of energy within the atom.

The energies of X-radiations differing widely in penetrating power are approximately if not accurately proportional to their total ionising powers.

Details of these investigations will be published shortly. C. G. BARKLA.

Physical Laboratory, The University,
Edinburgh, February 8.

The Green Flash.

So much has been written about the green-ray at sunset that I am somewhat diffident about adding anything. But as I find myself unable to accept the orthodox explanation of the phenomenon usually seen I write this note. This phenomenon, as seen by me on several occasions during the last summer on my way to Australia, always consisted in the last segment of the red sun before disappearance becoming a bright green (without any transition through intermediate tints); this green was as nearly as could be judged the complementary to the red of the sun itself. On one occasion I shut my eyes immediately after the green tint appeared, and it remained visible. There could be no doubt that what I saw was the purely subjective after-image of the disappearing segment of the sun. Of course, if this is so, it should be easy to set up a laboratory experiment to imitate the natural phenomenon; and on returning I asked Mr. E. Talbot Paris, research student in this department, to arrange an experiment in illustration. An eccentric hole was made in a disc mounted on an axle. Red glass or gelatine film was fixed over the hole, and a bright light placed behind illuminated the film and produced thereby a miniature sun, which by slow rotation, could be made to "set" behind an interposed card. At the instant of setting, the artificial sun exhibited an exact reproduction of the phenomenon of the green-ray. It was easily possible in this way to obtain a red-ray using a green sun, or a blue-ray with a yellow sun, and so on.

It is easy to give the rationale of the effect. The positive light gradually diminishes as the artificial

sun passes below the horizon; and it only requires a little adjustment of the rate of disappearance in order that the negative after-image excited at a previous instant when the segment was brighter, shall overpower the simultaneous weaker positive image of the remaining segment itself.

It would not be fair for me to dogmatise and assert that this is the only phenomenon which comes under the head of the green-ray. But it is certainly the only one which I succeeded in seeing; and it must always be present even on the possible rarer occasions when colour changes arising from dispersion are also evident. It is certainly also what many others saw. At the same time, it must be added that the phenomenon as observed by different persons, even on the same night, was so variously described as to lead one to suppose that the subjective element is sometimes present to even a greater degree than is implied in the above note. ALFRED W. Porter. Physical Department, University College, London, February 7.

Trenching Ground and Spraying Potatoes.

IN the notice in NATURE, of February 4, of the fourteenth report of the Woburn Experimental Fruit Farm it is suggested that the negative results obtained by us in bastard trenching might have been different had we experimented on vegetables, instead of fruit trees. No doubt the suggestion is correct; and a chance observation last year gave a striking illustration in point. Brussels sprouts were grown in a piece of ground partially occupied by trees; the ground had all been dug, but there were four patches of about four square yards each where it had been practically trenched, by the removal of trees and the digging out of their roots. In each of these patches the sprouts were two to three times larger than those in the intermediate dug ground. Universal experience indicates that a good depth of rich soil is essential for successful vegetable growing; this can only be obtained by trenching and liberal manuring, and nothing in our results should be taken as discountenancing such a practice.

It is also suggested that we should accumulate results on potato spraying to see whether such treatment pays on the average. We are doing so, and those already obtained are nearly sufficient for the purpose. They extend over eight seasons, and are on a fairly large scale, though the diversity in conditions, adopted for other reasons, renders it somewhat difficult to deduce a fair average from them. As it stands, this average is 7.8 per cent. increase on the weight of sound tubers as a result of spraying. Putting the average yield at 7 tons to the acre, and the net price realised at 31. 10s. per ton, the value of the increment will be l. 18s. Two sprayings would cost, for materials, labour and use of plant, about 18s. to 1l. 138., according to the substance used, and this would leave a margin of profit of from 5s. to 20s. per acre.

Harpenden, Herts.

SPENCER PICKERING.

Early Representations of the Giraffe. THE discussion in NATURE during the past year concerning the first mention in literature of the opossum and kangaroo has suggested a similar inquiry with regard to certain other well-known animals of the New and Old World.

When one examines into the sources whence were derived the illustrations in early printed books on

natural history, it is found that many are copied after drawings in old manuscripts.

A good example is furnished by Conrad Gesner's figure of an ichneumon, taken from an ancient MS. of Oppian, as the author declares.

FIG. 1.-Giraffe from mural painting at Villa Pamfili, near Rome. (After Keller, from Jahn).

In the case of the giraffe, what is thought to be the earliest portrait taken from life and engraved in a printed book, occurs in a work published in 1486 by Bernard de Breydenbach, a canon of Mayence, under the title of "Opusculum sanctorum perigrinationum." The figure is, however, inferior to those

FIG. 2.-Giraffe and Cercocebus, from ancient Egyptian monument at Thebes. (After Ehrenberg).

of the same and other African mammals which are introduced in the Ebsdorf and Hereford maps of 1282. Pictorial representations of the giraffe by Roman artists have been preserved from the time of classical

antiquity, and still earlier designs have come down to us in the form of ancient Egyptian hieroglyphics and inscriptions. That some of these were remarkably faithful likenesses may be judged from the two accompanying figures, one of which is reproduced from O. Keller's "Die antike Tierwelt" (1909), and the other from a memoir by C. G. Ehrenberg, "Ueber dem Cynocephalus und den Sphinx der Aegypter," published in 1834. C. R. EASTMAN.

American Museum of Natural History.

The Economic Status of the Blackcap. MR. COLLINGE does not meet the question whether the good the blackcap does in the spring balances the value of the fruit it takes in the summer. But he mentions having found a few aphids in the stomachs even in the fruit season, from which it may be inferred that more would be eaten, when there was no fruit in the spring. Now considering the enormous reproductive powers of the female aphis and that every female destroyed in the spring represents a diminution of many hundreds of the most mischievous pests that the farmer has to contend with in the summer, it seems only reasonable to conclude that the bird does at least as much good as harm. But the latter is seen while the former is not.

Ulcombe, Kent, February 5.

ALFRED O. WALKER.

My experience of the blackcap is that the good it does in the spring by no means balances the harm it does during the rest of the year in fruit-growing districts.

The aphids found in the stomachs were all pea lice (Macrosiphum pisi, Kalt.), and were probably obtained accidentally when feeding upon peas.

I have elsewhere pointed out (Journ. Board Agric., Sept., 1912) that all birds, other than doves and pigeons, feed their young upon an animal diet, of which insects form a large proportion, whatever may be the character of the food of the adult; the blackcap would, however, seem to form an exception, judging from the four nestlings I examined, whose stomach contents consisted of seeds or remains of fruit and fruit pulp. WALTER E. COLLINGE.

8 Newhall Street, Birmingham.

The Rusting of Iron.

I Do not know if any account of experiments such as the following on the rusting of iron has appeared in print before, but if not they may be of interest to others of your readers besides myself. Briefly, they are as follows::

(a) A small flask (100 c.c. flask with long narrow neck does well) is filled to the bottom of the neck with potassium ferricyanide solution, and then the neck is filled to the top with ordinary water. A long bright iron nail is then suspended in the water without disturbing the ferricyanide solution, and in a few minutes a blue colour will make its appearance in the neighbourhood of the boundary between the water. and the ferricyanide. The formation of Turnbull's blue goes on regularly, and it settles to the bottom instead of iron rust.

(b) A bright iron nail is placed at the bottom of a solution of potassium ferricyanide in a similar flask, and in a short time spots of blue make their appearance on the nail instead of the usual deposit of iron

rust.

The explanation according to the ionic theory seems obvious. E. J. SUMNER. The Grammar School, Burnley, Lancs, February 5.

OF

STAR CLUSTERS.

F all the telescopic objects in the sky none are more beautiful or more fascinating than the condensed, globular star clusters. Their bewildering complexity renders them unsuitable for direct study at the telescope, but photography has now brought them within the range of systematic investigation. The technical problem which they present is by no means easy, and demands high resolving power for success. The fine examples reproduced herewith, M3 and M13, have been very kindly sent from the Mount Wilson Solar Observatory, and illustrate admirably the work of the famous 5 ft. mirror constructed by Mr. G. W. Ritchey.

Cer

Considerable attention was given to the star clusters by Sir John Herschel, whose attempts to depict them by hand met naturally with small success. tain curious irregularities which he believed to exist in the distribution of the stars may be attributed to a purely subjective origin, or they may be accounted for by the absorptive influence of external dark nebulous masses. No great importance is now attached to them, and in the main the stars may be considered as distributed with radial symmetry. But one curious feature noticed by Sir John Herschel has been confirmed by later study. The stars in a cluster tend to divide into two classes of magnitude, a brighter and a fainter, separated by a distinct interval. Can this be a visible division of stars presumably at the same distance and of nearly equal age into the two classes of giant and dwarf stars inferred by Hertzsprung and H. N. Russell?

About twenty years ago Prof. S. I. Bailey, at that time at Arequipa, devoted considerable study to photographs of the chief globular clusters. His work proceeded on two lines. On one hand he made systematic counts of the stars recorded, thus laying the foundation for statistical investigations of their rangement in space. And on the other he investigated the magnitudes of the stars, and was thus led to the remarkable discovery that several clusters contain a high proportion of variable stars, a ratio of 1 in 7 in the extreme case of M3. His detailed results for the clusters ய Centauri and M3 have been published in two beautiful memoirs. The type of variation is of a distinct character, though a few isolated examples have been found elsewhere in the sky, with a period of about twelve hours and a rapid rise to maximum. In the case of M3 the variation is sin- | gularly true to one type, the range between maximum and minimum being two photographic magnitudes. Some clusters, notably M13, are almost entirely devoid of such variables; where they do

occur they are apparently confined to the stars of the brighter order of magnitude.

The question of the distribution of stars in clusters was discussed by Prof. E. C. Pickering. Using counts on the clusters Centauri, 47 Tucane and M13 (Herculis), he formed the important conclusions: (1) that the law of distribution is essentially the same for different clusters, (2) that the bright stars and the faint stars of a cluster obey the same law. He represented graphically the curve of apparent (projected) density for different distances from the centre, and attempted without success to reproduce it by assuming laws of the form 1-2 and (1-r)" for

FIG. 1.-M3 Canes Venatici. Exposure 4h.

the density in space. The latter form was also tested by Mr. W. E. Plummer with much the same result on an extensive series of measures of the stars in M13.

The next important contribution to the subject is due to H. v. Zeipel, who measured the positions of the stars in M3 (Can. Ven.). By adapting the solution of a certain integral equation studied by Abel he showed how the law of distribution in space may be deduced numerically from the observed distribution as it is seen in projection. Later he compared the law of density in space arrived at in this way with that which obtains in