56o 



NA TURE 



[April i6, 1908 



>'ht be mistaken for a red unless closelv 



such a roan 

 examined. 



Here, then, is one of our most distinguished breeders 

 referring to substitution, and making an error of descrip- 

 tion as regards the colour of a calf. 



The last time I visited the farm where the above " red " 

 bull is standing I saw some white calves, and this after- 

 noon one of them, now si.\ or eight weeks old, was miss- 

 ing. I asked the owner what had become of him, and got 

 the reply, " I have sold him." This particular white calf 

 may be referred to in the Herd-book by his breeder, but 

 many another similar one is never referred to at all. 



Prof. Pearson suggests that, if there are inaccuracies and 

 misstatements ui the Herd-book, " Mendelism cannot be 

 discussed on the basis of the Shorthorn data." I do not 

 agree. But, if not Mendelism, can biometric theories be 

 (iiscussed upon the same data? 



The latter half of Prof. Pearson's letter does not bear 

 much upon the present issue, but I should not be astonished, 

 if his theories as to colour determinants and parti-colours 

 are followed up, that each of the two races from which 

 the Shorthorn is descended should split up into mori' than 

 one variety. 



Prof. Pearson thinks that, because I neglected the figures 

 in the first part of his original paper, I was evading some 

 of the data. This is not so. I did not notice that they 

 comprised other data, for which 1 am sorry, because the 

 ninety-one white crossings which gave eighty-six white 

 calves, four roans, and one red, would have been helpful. 

 I had not seen the original paper since the time it was 

 published two years ago, and, when I conceived the idea 

 that Shorthorns are Mendelians, I went straight to the two 

 tables from which I quoted, in the belief that they con- 

 tained all the relevant data collected by Miss Barrington 

 and Prof. Pearson. James Wilson. 



Royal College of Science, Dublin, April R. 



The Nature of 7 and XRays. 



If I am putting the correct interpretation on Mr. 

 Barkla's letter in Nature of February 6 (p. 319), I have 

 to thank him for the admission that his experiments are 

 not so contrary to the neutral pair theorv as he had at 

 first supposed. 



Mr. Barl-cla still concludes, however, in favour of the 

 ether pulse theory. He has compared the intensities of 

 two secondary beams emitted by carbon under the influence 

 of an unpolarised primary beam, the one returning on 

 the track of the incident rays, the other moving in a 

 perpendicular direction. His calculated ratio is 2:1; 

 experiment gives 1-85 to i (Phil. Mag., February, p. 293). 

 Such an agreement has its value. But, at the same 

 time, he finds that for harder rays the ratio drops to 

 I 45 to I, with no sign of a limit. His theory is unable 

 to predict this decline, far less to measure its amount. 

 It is no compliment to the ether pulse theory to describe 

 such incomplete successes as " absolutely conclusive 

 evidence." 



He invites me to suggest a theory of scattering which 

 shall have as much success as. his own. But, on the 

 neutral pair theory, the laws of scattering must depend 

 directly on the constitution of the atom, as to which it is 

 scarcely possible to do more than speculate. It is not 

 incumbent on me at this stage to frame an independent 

 hypothesis by the success of which my older one is to be 

 judged. 



He wishes to avoid arguments founded on an experi- 

 mental study of the 7 rays. But it is quite legitim.ate to 

 begin with the 7 rays, and to carry the argument over to 

 the X-rays, on the ground that there is an extremely close 

 parallelism between the two types. Evidence of this sort 

 I'.innot be avoided by resolutely facing the other way. 



It will perhaps conduce to greater clearness if I state 

 IV position briefly. 



11) Nearly a year ago I pointed out that almost ,ill the 

 'ii'iuimena of 7 and X-rays could be explained on a 



vitral pair theory at least as well as on an ether pulse 



"ory. This applied particularly to all effects connected 



iih the production of secondary kathode rays of high 

 velocity, effects which are at the root of most of what 

 has been observed. 



XO. 2007, \OL. 77] 



(2) I have recently described some experiments carried 

 out by Dr. Madsen and myself which seem to me to sup- 

 port my contention in the strongest way as regards the 

 7 rays. 



(3) Since X-rays and 7 rays resemble each other so 

 faithfully in most respects, particularly those connected 

 with the high-speed kathode rays, I have therefore sug- 

 gested that the experiments also support my contention 

 regarding the nature of the bulk of the X-rays. 



{4) There are a few outstanding phenomena of the X-rays 

 which do not fit in so readily with a neutral pair hypo- 

 thesis, particularly Manx's velocity experiment, and the 

 diffraction experiments of Haga and Windt. These seem 

 to prove the existence and activity of ether pulses. .-\s 

 regards Mr. Barkla's polarisation effects, I have indicated 

 a possible way of explaining them on the neutral pair 

 theory ; but I am quite content to wait for the guidance 

 of future experiments, amongst which Mr. Barkla's recent 

 work will take its proper place. 



(5) If 1 admit the existence of ether pulses, I do not 

 thereby weaken my contention that the most important 

 and effective part of 7 and X-ray radiation is 

 material. We know that ether pulses exist ; it does not 

 follow that they do everything. On the contrary, the 

 evidence for the ether pulse theory is extremely weak in 

 just this direction ; there is a danger that the \iost hoc 

 has been confused with the propter hoc. When I see a 

 boy jerk his arm, and hear immediately afterwards a 

 rattling on my roof, I know quite well that the motion of 

 the boy's arm has set an air pulse going, but I do not 

 conclude that one of my chimneys was in a dangerously 

 explosive condition, and that the air pulse has precipitated 

 the violent discharge of half a brick. 



W. H. Bragg. 



The University of .Adelaide, South .\ustralia, 

 March 12.' 



The Corrosion of Iron and Steel. 



.•\ PAPER describing the investigation of the causes of 

 rusting of iron was read in May, 1907, before the New 

 York Section of the American Chemical Society by Mr. 

 William H. Walker and others, and has been recently 

 printed in this country. After criticising the various ex- 

 planations which have been put forward of the rusting of 

 iron in contact with water, the authors approve the sugges- 

 tion of Whitney that the first step in the process is the 

 escape into the liquid of iron in the form of positively 

 charged ions. In confirmation of this, the authors stale 

 that they succeeded in detecting iron by chemical tests in 

 water which contained only a trace of electrolyte, and was 

 free from o.xygen and carbon dioxide, after the Avaler had 

 been in contact with iron. 



Such an explanation would apply to a fact which con- 

 fronted me some years since when investigating the cause 

 of the action of water on lead. Every precaution was 

 adopted to bring a surface of metallic lead absolutely fre" 

 from oxide into contact with water free from dissolved 

 gases, with the expectation that if these conditions were 

 fully complied with no lead would pass into solution. In 

 the course of the investigation the precautions which were 

 taken to secure the conditions specified gradually became 

 more stringent, and the amount of lead passing into solu- 

 tion was correspondingly reduced ; but when the utmost 

 possible care had been taken, lead in very minute propor- 

 tion was still detectable in the water by chemical tests. 

 It is of interest to note that the proportion of lead was 

 constant when the contact of water with lead had been 

 brought about in repeated experiments with some variations 

 in detail. The impression produced by these results on 

 my own mind was that undoubtedly lead in the metallic 

 state must have passed into the water, and upon re- 

 consideration of the experimental work and its results I 

 feel satisfied that this was the case, and that the lead 

 probably passed into the water as iron did in the experi- 

 ments made by Whitney and repeated by the American 

 investigators, when they brought iron into contact with 

 water under conditions similar to those which I had 

 secured. Frank Clowes. 



The r.range, Dulwich. 



