November lo, 1923] 



NA TURE 



687 



Long-range Particles from Radium-active 

 Deposit. 



In a letter to Nature of September 22, p. 435, 

 under this heading, L. F. Bates and J. Stanley Rogers 

 suggest that the H-particles found by us (Nature, 

 September 15, p. 394) to become expelled from the 

 atoms of Be, Mg, and Si, probably also of Li, by 

 a-particles, are really identical with the long-range 

 a-particles which these authors have obtained from 

 radium C deposited on a brass disc. Highly interest- 

 ing as their communication is, it does not, however, 

 seem to have any direct bearing on our results. 



The difference in brightness between the scintilla- 

 tions from a-particles and from H-particles viewed 

 under identical conditions is so conspicuous, that no 

 mistake is possible. Comparing the former to stars 

 of the first magnitude, the latter would be of about 

 the third magnitude ; that is, a ratio in luminosity 

 of about 6 to I . By way of emphasising this difference 

 we have, in the same scintilloscope, demonstrated the 

 scintillations due to the H-particles from aluminium 

 foil inside a glass capillary charged with emanation, 

 together with the scintillations from polonium 

 a-particles, before the physical section of Skandina- 

 viska Naturforskaremotet, held in Gothenburg this 

 summer. With due precautions the same experi- 

 ment can also be carried out with a thin-walled 

 silica capillary containing a few millicuries of emana- 

 tion, so as to demonstrate the H-particles from 

 silicon. Although there is very little doubt that the 

 scintillations we have observed are really due to 

 H-particles, an experimentum cruets can, of course, 

 be made only by measuring their magnetic and 

 electric deflection. 



As was stated in our first communication, our 

 final experiments were carried out with a minute 

 emanation vessel divided into several communicating 

 compartments of equal length, in which thin layers 

 of different substances were spread over the bottom, 

 made from thinnest copper foil. Control countings 

 of the particles expelled from the naked copper foil 

 of an empty compartment proved the number of 

 these to be only a fraction of those expelled from the 

 compartments charged with other substances. As the 

 absorption curve for the " copper "-particles agreed 

 with a theoretical absorption curve calculated for 

 natural H-particles from hydrogen supposed to be 

 occluded in the copper, there seems to be no reason 

 for assuming them to be expelled directly from dis- 

 integrating atoms of radium C, But even if that 

 were granted, there is no reason for ascribing that 

 origin to the much more numerous particles of 

 relatively short range expelled from the Be, Mg, 

 and Si compartments of the same vessel, considering 

 that the amount of emanation and its products 

 present within each compartment was practically 

 the same. 



As a matter of fact a small number of scintillations 

 of a-type was generally observed in our experiments, 

 beside the much fainter H-scintillations, especially 

 at the lowest values of absorption, when they were 

 relatively numerous. We have .so far not had occasion 

 to examine these particles or their origin but have 

 for the time being assumH them to be identical with 

 the particles found ICrnest Rutherford to be 



expelled from oxy^ Mag. vol. xxxvii. p. 562) 



which have in succession been taken for oxygen 

 atoms carrying a single charge, double charged X 

 nuclei, and now, apparently, a-particles of abnormally 

 long range. 



In conclusion, we may say that, judging from the 

 experimental data at present available to us, we 

 cannot see any other way of explaining the origin 



of the particles we have observed than by upholding 

 our former view, namely that they are H-particles 

 expelled at an artificial disintegration of the beryllium-, 

 the magnesium-, and the silicum- (probably also the 

 lithium-) atoms and not any long-range particles 

 from radium-active deposit as the title given by the 

 Editor to our first letter would seem to suggest. In 

 that letter, in addition to the corrections pointed out 

 in N.\TURE of October 13, p. 540, the word " neutral " 

 should have been printed "natural." 



Gerhard Kirsch. 



Hans Pettersson. 

 October 13. 



Colour Vision and Colour Vision Theories. 



Whether Prof. Peddie's explanations are adequate 

 is a matter for the reader to decide. Let us take one 

 of a fact which is conclusive evidence against the 

 trichromatic theory. If the terminal portion of the 

 red end of the spectrum be isolated in my spectro- 

 meter it will appear as a faint red upon a black 

 background. If the eye be fatigued with red light, 

 even by looking through a red glass held against a 

 light for one second, the red will not be visible for 

 some considerable time, but the eye may be fatigued 

 for twenty minutes with yellow light without inter- 

 fering with the visibility of the red light. 



Prof. Peddie's explanation is as follows : " That 

 there is no shortening at the red end of the spectrum 

 after fatigue with yellow light follows at once if both 

 the red and the green sensations are fatigued by the 

 yellow light, while all three sensations, red, green, 

 and blue, are present to some extent at all visible 

 wave-lengths." But this explanation, which is in- 

 consistent with the work of Konig, Abney, and others, 

 does not explain why there is considerable shortening 

 after slight fatigue with the red glass. Prof. Peddie 

 does not explain Shelford Bidwell's crucial experi- 

 ment, namely, that his red borders are not seen 

 with spectraf yellow light but are seen with a mixed 

 yellow made up of red and green matching it. 



As with other departments of science, the minutest 

 accuracy is required in experiments on colour vision. 

 Many results are due to impure colours and stray 

 light. A chemist would not do Marsh's test for arsenic 

 when he had bought his zinc at an ironmonger's 

 and his sulphuric acid at an oil shop, both being 

 contaminated with arsenic, but many workers are 

 satisfied to use coloured papers for work on colour 

 vision. 



If the positive after-imaf,'e of a spectrum be viewed 

 it will be seen to disappear iVoiu ilic red to the violet 

 end, and on the trichromat ir theory it is stated that 

 the positive effect of the ikI sensation disappears 

 before that of the green ; but in an absolutely dark 

 room, if pure spectral yellow light be thrown on a 

 white screen and a flicker apparatus rotated slowly 

 in front of it, the yellow will not change its hue ; on 

 the trichromatic theory it should become green. 

 The results are quite different when stray light is 

 allowed to fall on the screen as well. 



F. W. Edridge-Green. 



London, October 27. 



Sex Chrotnosomes in Plants. 



I HAVE recently been investigating the cytology of 

 a number of dioecious plants with the intention, if 

 possible, of throwing light on the matter of sex 

 chromosomes in plants. Incidentally, I took up the 

 genus Lychnis, one species of which, Melandryum 

 rubrum, Garcke (/.. dioica, L.), has been examined pre- 

 viously by Strasburger. In detailing his observations 

 he states that, in both sexes, there are twelve pairs 



NO. 2819, VOL. 112] 



