October 6, 1904 



NA TURE 



55; 



LETTERS TO THE EDITOR. 



\The Editor does »o( Iwld himself rcspottsible for opinions 

 expressed by his correspondents. Seithcr can he undertake 

 to return, or to cornspond witli the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 A'o notice is taUen of anonymous communications.] 



Radio-activ.ty and London Clay. 



I VKNTLRE to think your readers may be interested in the 

 following results. 



The recent tube operations in London have brought to 

 the surface specimens of the London Clay from different 

 districts. Samples of this clay taken from such different 

 points as Hyde Park Corner, Brompton Road, and Haver- 

 stock Hill have been tested in the physical laboratory of 

 the .South-western Polytechnic for the presence of a radio- 

 active gas bv .Mr. H. Cottani, and he has been unable to 

 detect with his apparatus auy marked quantiiy of active 

 gas from the clays. 



With the same apparatus he has detected quite easily the 

 radio-active gas from the water of a deep well, belonging 

 to Messrs. Eastman, Latimer Road, \V., which goes below 

 the clay to the greensand. We have come to the conclusion 

 that the London Clay forms a floor through which the 

 radio-active gas does not penetrate ; or it may be said that 

 the radio-active substance only travels when the water with 

 which.it is associated can travel. This is an argument 

 in support of Prof. J. J. Thomson's view, that the radio- 

 active gas, w-hich he found in deep well waters, arises from 

 the splitting up of a trace of soluble radium salt which 

 comes up with the water. S. Skinner. 



-South-western Polvtechnic, Chelsea. 



Cecil's Gas Engire. 



Thf earliest practical gas engine appears to be unknown 

 to the leading writers on internal combustion engines. I 

 think that it may be a matter of interest to those who are 

 antiquarians in their subject — as Maxwell used to say — 

 to know that a working gas engine was shown in Cam- 

 bridge in the year 1820. It was the invention of the Rev. 

 W. Cecil, fellow of Magdalen College, Cambridge. A full 

 account of his engine is given in vol. i., p. 217, of the Pro- 

 ceedings of the Philosophical Society of Cambridge (paper 

 read November 27, 1820). The paper is long, and contains 

 excellent matter: a new form of parallel motion is de- 

 scribed, and what the author calls "ardent spirit" and 

 turpentine, and vapour of oil, are suggested as possible 

 substitutes for the gas employed by the inventor of the 

 ' ngine. F. J. Jervis-Smitii. 



Trinity College, Oxford, September 211. 



The Iris and the Colour Sense. 



Mr. \*incent Napier's communication in your issue of 

 .September i on " .\daptive Colours of Eyes " moves me to 

 record an observation which I have never seen formulated. 

 It is that persons who exhibit a fondness, in dress, for 

 striking colours, or display exceptional taste in colour 

 combination, have eyes of a pronounced and positive colour. 

 One naturally notices this chiefly in women, but I believe 

 it holds good for men also. In the nutter of harmonious 

 costuming, perhaps it would not be tcjn much to say that 

 many women dress conformably to the tint of the iris. 



New York, September 17. W. P. G. 



Electrolytic Oxidation. 

 I NOTICE with interest that in your issue of September 22 

 (p. 511) a brief account is given of a memoir published by 

 Paterno and Pannain in the Gazzetta on the electrolysis of 

 alkaline aqueous solutions of potassium cyanide. The chief 

 result of their work appears to be the production of 

 potassium cyanate. In the summer of 1.S09 a friend and I 

 were working in the same direction. From the commence- 

 ment of our experiments, on both aqueous and semi-alcoholic 

 solutions of potassium cyanide, we were struck by the almost 

 entire absence of oxygen in the electrolytic gases. The 

 aqueous solutions became strongly alkaline and ammoniacal. 

 The semi-alcoholic solutions became strongly alkaline, but 



not ammoniacal. .'Xcetamide was, however, detected in a 

 distillate, the presence of which may explain the absence of 

 free ammonia. The alcoholic solutions also yielded, on 

 evaporation, white crystals, which proved to be potassium 

 carbonate. 



We therefore assumed, without direct proof, that oxygen 

 had been absorbed by the potassium cyanide to form 

 potassium cyanate. This assumption, which now receives 

 confirmation, was based on the detection of its hydrolytic 

 products, w-hich we considered to have been formed accord- 

 ing to the following equation : — 



KCNO-|-2H,0 = KHCO, + NH3. 



It is possible that continued electrolysis would have led 

 to the production of potassium formate from the bicarbonate 

 (Berichte, xxxvii., 2836), if this change had not, to some 

 extent, already occurred. 



We obtained evidence of the formation of more complex 

 bodies, but have been unable, up to the present, to prosecute 

 further experiments. Herbert -A. Kittle. 



Leatherhead, Surrey, September 26. 



DEVELOPMENTS OF THREE-COLOUR 



PHOTOGRAPHIC PROCESSES.'^ 



I. 



IX reviewing the recent progress of the various pro- 

 cesses, direct and indirect, of the reproduction of 

 colours by photography, it is obvious that there is no 

 very remarkable advancement to report. The ultimate 

 aim of those who do fundamental work at this subject 

 is to formulate a method that shall automatically re- 

 produce the colours of the original, just as by means of 

 a camera and lens the form of the original is auto- 

 matically drawn in true perspective. The realisation 

 of this desideratum does not seem at hand. There is 

 no method of producing colour prints known that does 

 not need so much control in the working of it or 

 alteration of its results, that it would be incorrect to 

 regard the final products as simple photographs. The 

 skill and sometimes the taste of the operator, and the 

 nature of the appliances that he makes use of, have 

 an important effect upon the work. This fact may 

 lead to the idea that photographic methods of colour 

 reproduction are of little use. But by the aid of photo- 

 graphy results may be obtained that were impossible 

 before, either in their character or in the economy of 

 their production. Photography in portraiture is not 

 considered useless because the negative goes through 

 the hands of the retoucher. 



Of the direct methods of heliochromy, the inter- 

 ference method that was practically worked out by 

 Lippmann remains nothing more than an interesting 

 illustration of certain physical phenomena. The many 

 restrictions that limit its applications and the difficul- 

 ties that beset its practice are such that it can never 

 be expected to develop into a practical process. -After 

 a dozen years or so, Lippmann photographs are still 

 regarded as curiosities, and are interesting only as 

 examples of the method. None appear to have been 

 made for the sake of the subject. The restrictions as 

 to size and the angle under which they must be viewed, 

 the need for getting rid of reflections from -the surface 

 of the film, the slowness of their production, and, 

 above all, the uncertainty of the colours produced and 

 the fact that they change with any alteration in the 

 condition of the film, render the process useful to the 

 physicist rather than the photographer. 



The only other method of direct colour photography 

 that appears at all likely to develop into a practically 



1 "The Water-Colour Drawings of I. M. W. Turner. R.A., in the 

 National Gallery." By T. .^. Cook. Pp. vi-f.86 and 5S plates. (London: 

 C.nssell and Co., Ltd., 1904.) Price q guineas net. 



"Three-Colour Photography." By A. F. von Hubl. Translated by 

 H. n. Klein. Pp 148. (London : A. W. Penrose, Ltd., 1904.) 



"Photography in Colours." By R. C. Bayley. and edition. Pp. 151. 

 (London : IlifTe, Ltd., 1904.) Price is. net. 



NO. 1823, VOL. 70] 



