November 24, 1904] 



NA TURE 



83 



Observations of the Leonid Meteors, 1904. 

 Observations by the writer this year go to show that 

 the intensity was much below that of last. Briefly, the 

 nights of November 12 and 13 were heavily overcast, but 

 the night of November 14 and early morning of November 15 

 were fortunately clear. The display lasted about an hour, 

 say from 12.30 until 1.30 a.m., maximum i o'clock a.m. 

 (local times), hourly rate, low, 20 to 25. Bright meteors, 

 however, continued to appear at intervals up to 3 a.m., 

 when clouds coming on stopped further observation. A 

 couple of hours' watch before and after midnight of 

 November 15 gave only two Leonids, while another two 

 hours' watch on the night of November 16 showed the 

 radiant, which was sharply defined the previous nights, at 

 150° + 23°, near Zeta, to be quite quiescent. Other radiants 

 active were : — 



R.A. Dec. 



It would be interesting to hear of observations made 

 during the hour or so before daybreak on the morning of 

 November 15, as it is just possible the increased intensity 

 noticed in previous years may not be real, but due rather 

 to the fact of the radiant being near the meridian, and the 

 smaller meteors coming down more direct at that time are 

 the better able to penetrate to the lower layers of the atmo- 

 sphere. W. H. MlLLlGAN. 



Holywood, CO. Down, November 18. 



The Discovery of Argon. 



In your translation of Prof. Mendel^eff's interesting paper 

 an the chemical elements (November 17, p. 94) I see that 

 he attributes the discovery of argon and its congeners to 

 Ramsay. Am I not right in believing that it was Lord 

 Rayleigh who discovered argon, and that it was he who 

 gave that impulse to chemistry which Sir William Ramsay 

 has carried forward to such remarkable results? 



November 20. G. H. Darwin. 



Blue-stained Flints. 



Some years ago there were many blue-stained flints on a 

 road near Cambridge. Lime from gas-works was about 

 to be mi.\ed with the flints used as road-metal, and the two 

 different materials had lain for some time in heaps by the 

 roadside. The blue colour, in some instances very intense, 

 was developed wherever a heap of flints and one of lime 

 touched each other ; from which I surmised that the calcium 

 sulphide of the gas-lime had reacted with an aluminium 

 compound present in the flints, producing a substance akin 

 to ultramarine. F. J. Allen. 



Cambridge, November 19. 



Inheritance of Acquired Characteristics. 



It may be worth noting that since my letter to you of 

 some months back, in which I gave an instance of fox- 

 terrier pups being born with short tails, I have heard of 

 two similar cases. In one of these cases the dog was owned 

 by one of the managers of the Rhodes' Fruit Farms, near 

 Cape Town. The other case occurred in the Transvaal at 

 Sabi, one out of a litter of four being born with a short 

 tail. D. E. Hutchins. 



Forest Office, Cape Town, October 18. 



DR. KOENIG'S METHOD OF COLOUR 

 PHOTOGRAPHY. 

 T N the methods of three-colour photography hitherto 

 ■'■ practised the colours are used as inks, stains, or 

 pigments already prepared, and their distribution is 

 effected indirectly by the action of light. In the imbi- 

 bition process tliree thin gelatin reliefs are prepared 



NO. 1830, VOL. 71 



(using potassium bichromate to sensitise the gelatin), 

 and after each relief is stained with its appropriate 

 colour the thfee films are superposed. The method 

 recently described by Dr. Koenig is of the multiple 

 film kind, but the colours are produced by direct ex- 

 posure to light. 



Many organic colouring matters yield by reduction 

 colourless bodies that are more or less easily re-oxidised 

 with the production of the original colours. The 

 oxidation of these leuco colouring matters is generally 

 if not always quickened by light. If, therefore, the 

 leuco-compound produced from a dye of a suitable 

 red colour is caused to impregnate a film, and this is 

 exposed beneath the negative made to give the red 

 image in three-colour work, the red image may be 

 produced by direct exposure to light. A similar pro- 

 cedure will of course give the yellow and blue images, 

 and so the complete colour print may be obtained. 

 Such are the general principles upon which Dr. 

 Koenig's process depends, but to elaborate the details 

 of a successful process on these lines it was necessary 

 to overcome many practical difficulties. 



It was necessary, in the first case, to select only those 

 dyes (of suitable colours, of course) that yield leuco- 

 derivatives of sufficient stability to stand the necessary 

 manipulations. Then it was found that the leuco- 

 bases selected as otherwise suitable gave but a feeble 

 image even after long exposure ; but it was observed 

 that when collodion was used as the medium the 

 sensitiveness was greatly enhanced, and the vigour of 

 the image very much improved. This improvement 

 was traced to the action of the nitrocellulose, and other 

 nitric acid esters were found to have a still greater 

 effect. Nitromannite especially is useful for sensitising 

 purposes. Dr. Koenig emphasises the fact that the 

 leuco-bases in an inert film are useless, as the action 

 of aerial oxygen, when it has reached its maximum, 

 gives only a flat and feeble image. 



The fixing of the image was the next difficulty, for 

 obviously it is necessary to remove the excess of the 

 leuco-bocly without interfering with its coloured 

 oxidation product. It is well known that many dyes 

 show a great tendency to remain attached to a fabric 

 or film in spite of the' application of solvents, but the 

 leuco-bases employed also have a similar tendency. 

 Dilute mineral acids, tliough they dissolve the greater 

 number of the leuco-bases, would not remove them 

 fro- ^ collodion films. A 10 per cent, solution of mono- 

 chlorac3tic acid was found to be the best fixing agent. 



The various solutions required are supplied ready for 

 use, and the following summary of the instructions 

 issued with them will give a general idea of the 

 manipulation required. A piece of baryta coated paper 

 rather larger than the negative has its edges turned 

 up, and iscoated with a li per cent, collodion to which 

 has been added the leuco-derivative of the blue dye and 

 a solution containing the necessary additions. When 

 dry it is exposed under the appropriate negative (for. 

 say, twenty to forty seconds in bright sunshine), soaked 

 in the fixing bath for a few minutes, washed for a few 

 minutes, dipped into a gelatin solution that contains 

 a little chrome alum, and hung up to dry. The print 

 is then turned so that its lower edge shall be upper- 

 most, again dipped into the gelatin solution, and again 

 allowed to dry. The gelatin coating is applied to 

 isolate the collodion film so that it may not be interfered 

 with by the application of the second collodion. The 

 print is then coated with collodion to which the 

 materials for the blue image have been added, exposed 

 under the proper negative, fixed, and coated twice with 

 gelatin as before. A similar procedure follows for_ the 

 yellow image, and after the final gelatin coating it is 

 well to varnish the print. It is claimed for the dyes 

 employed that the blue, which is the one most liable 

 to change, is more permanent than Prussian blue. 



