June 19, 1913] 



NATURE 



397 



LETTERS TO THE EDITOR. 

 [The Editor does not hold Iiimself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 tliis or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Pianoforte Touch. 



I have read Prof. Bryan's piano-player article in 

 Nature, and wish to congratulate him on seeing so 

 early the wonderful capacity of the pneumatic player. 

 v agree with him. Long ago I have done work 

 like his, though very crudely. Thus I always played 

 with the feet, sitting on a pivoted swinging chair, 

 and I constructed an arrangement in which, by means 

 of two strings, I had some control of the touch. It 

 was a partially successful attempt at most. I also 

 fixed up a "dead stop" string' operating a brake on 

 the engine, by which pauses could be made at the 

 proper places. I am sure Prof. Bryan's way is 

 immensely superior. 



It is very singular that some of the compound touch 

 problems are of a transcendental nature. They cannot 

 be solved bv common, rigorous mathematics, but only 

 by my new mathematics. At Prof. Perry's suggestion 

 I made this a feature of one of my books. 

 It was full of compound touch problems in- 

 soluble (so I was told) by rigorous mathe- 

 matics, though the rigorous mathematicians cannot 

 deny the results. It is because their ideas concerning 

 functions are not broad enough. I have also been 

 thinking about the theory, and think it will be more 

 difficult than appears in Prof. Bryan's paper, because 

 his touch variations are secondary to those of the 

 player itself, due to the way the holes are cut and their 

 overlap in the music-rolls. The results are sometimes 

 not good. Another thing, I have considered the piano 

 itself to be a rather imperfect instrument. We get 

 used to its faults ; is that any reason they should be 

 made virtues? 



I consider the piano-player does for music what the 

 printing press did for books. But while, after read- 

 ing a book once, you generally never wish to read it 

 again, it is impossible to appreciate elaborate tech- 

 nical compositions without playing them over and 

 over again. So there is something to be said for the 

 olaving by children and men even in the most 

 mechanical and unintelligent war. 



Oliver Heayiside. 



A Peripheral Effect with X-Radiation. 



Whilst repeating the now well-known experiments 

 of Barkla, Laue, and others we have accidentally 

 met with some remarkable effects upon which we 

 should like to invite judgment. By inadvertence the 

 edge of a piece of mica intercepted a direct beam of 

 X-rays, and the recording photographic plate shows 

 pronounced black and white bands along the X-rav 

 shadow of the edge of mica. Further experiments 

 with mica, glass, and metals also gave the effect, the 

 edge of the shadow being bounded by a well-defined 

 black band in the dark portion of the field with a 

 light band in the lighter half. 



An extended series of experiments was then made 

 using lead foil cut into thin strips from one to five 

 layers in thickness, mounted on glass, and placed in 

 the direct beam of X-rays ; no screen of any kind 

 being employed, as was the case in the preliminary 

 experiments. The distance of the photographic plate, 

 placed behind and parallel to the mounted pieces of 

 lead, was varied from 3 mm. to 5 cm., and that of 



NO. 2277, VOL. 91] 



the anti-kathode to the obstacle from 26 to 450 cm. 

 Under these varied conditions of distance dark 

 and light bands along the edges were obtained on the 

 negative. The X-ray bulb had a fine focus, and 

 exceedingly sharp X-ray shadows were obtained, 

 especially at distances between 200 and 450 cm., a 

 fact to which the observance of these bands is greatly 

 due. 



The width of the bands in these lead strip experi- 

 ments is roughly 01 to 0-2 mm., but in the preliminary 

 mica and glass experiments they were much broader, 

 being about 05 mm. in width. These bands are' dis- 

 tinctly visible under a low-power microscope, whilsl 

 under favourable conditions of illumination they are 

 plain without artificial aid, and the same remarks 

 apply to their prints. They are seen also when 

 thrown upon a screen, and these facts seem to pre- 

 clude the suggestion of their being contrast or optical 

 effects, as was supposed by Haga and Wind in their 

 well-known attempts to demonstrate diffraction. 

 That they are not diffraction effects comparable with 

 those of light is shown by their not varying appre- 

 ciably in width as the photographic plate is varied 

 behind the mounted strips of lead foil. Nor should 

 these bands be confounded with those which appear 

 upon the portion of the beam reflected from crystal- 

 line surfaces (which we also obtained), and havi beet 

 described by de Broglie and Lindemann ; although 

 we are disposed to admit a possible physical connec- 

 tion. 



Bands of similar width and appearance have been 

 obtained with other metals, such as iron, zinc, copper, 

 and aluminium, and in one case when- an attempt 

 was made to obtain direct refraction the white band 

 appears between the transmitted and the direct beam. 

 The apparent constancy of width and appearance 

 under widely different conditions is a baffling point, 

 arguing prima facie an optical or photographic effect. 

 Yet against this is to be set the fact that so far mica 

 and glass have given bands several times as w-ide a? 

 those from metals. 



Attempts to vary the bands from metals by passing 

 electric currents through them, and by high tempera- 

 tures, have given so far negative results, though it 

 may be desirable to mention the fact that in the latter 

 case images of cold wires appear distinctly brighter 

 in the negative. In one experiment, in addition to 

 bands, a remarkable halo appears at a distance of 

 i-q cm. from the image of the circular orifice in a 

 metal screen. In another case a black band of ap- 

 proximately equal intensity to the image given by 

 the direct beam appears surrounded by a white area, 

 and in the same position, i.e. between the direct and 

 reflected images. The fact that this band is black 

 in the negative shows that the effect cannot be due 

 to absence, in this position, of the generally scattered 

 radiation which may have fogged the plate. 



An explanation of grounds of halation, or reflection 

 from the back of the plate, is, we need scarcely say, 

 inconsistent with the accepted theory of X-radiation. 

 The solution to which we may be reduced is 

 that the bands are due to some edge or peripheral 

 condition of the substance depending upon abrupt 

 discontinuity of the media (mica, air), since a mere 

 scratch or break in the surface does not produce the 

 bands. Increase of density along the edges due to 

 surface tension would appear to be of too small an 

 order to account for the phenomenon. A subjective 

 appearance of bands may invalidate some of the cases 

 with metals, but in others (especially that with a halo 

 suggestive of an X-ray spectrum) actuality is beyond 

 doubt. W. F. D. Chambers. 



I. G. Rankin. 



qo Gordon Road, Ealing, W. 



