July io, 1913] 



NATURE 



477 



pressibility of elements, amongst other fai ts, 

 it is evidently possible to influence intra-atomic 

 activity by means of forces applied from with- 

 out. It sCcms probable, therefore, that pressure, il 

 •sufficiently great, could be transmitted to the interior 

 of a uranium atom and supply the countervailing force 

 required to help the atom past a position of in- 

 stability. Once we realise this probability, we see 

 a cogent reason why the interior of the earth should 

 be free from radium and all other radio-active sub- 

 stances the formation of which from heavier elements 

 demands an increase in volume, these heavy elements 

 being at great depths only potentially radio-active. 



From this point of view radio-activity is, as Dr. 

 Schiller suggests, "an acquired habit of the sub- 

 stances that exhibit it," the habit being acquired when 

 such an element passes by any means whatever from 

 great depths below the earth's surface to regions of 

 less pressure. 



In a paper just issued in the Records of the Geo- 

 logical Survey of India (vol. xliii., part i) I have given 

 a preliminary account of these speculations concerning 

 the mineralogical constitution of the earth's crust, and 

 in a final paragraph have appended a brief reference 

 to this question of the inhibition of the disintegration 

 of uranium at great depths below the earth's surface. 



L. L. Fermok. 



Pianoforte Touch. 



In connection with the discussion on this subject 

 originated by Prof. Bryan's paper, I may mention 

 that I have been making some measurements during 

 the past winter with the view of obtaining some idea 

 of the velocities and forces involved in the motion of 

 the transmitting mechanism. By fitting an electric 

 chronographic arrangement to an upright piano I 

 have been able to measure the actual times taken in 

 different stages of the movement with different degrees 

 of loudness. 



Among other results, I have found that the time 

 during which the hammer is flying freely towards 

 the string after losing contact with the propelling 

 mechanism varies from about 0-04 sec. for />/> to 

 o-ooi sec. for ff. The distance of flight was about 

 1 cm., so the velocity ranged from 25 to 1000 cm. 

 per sec. At the latter extreme, however, the force 

 used in striking the key was greater than would be 

 used in ordinary playing. On the other hand, when 

 a weight was allowed to fall on the key from the 

 smallest height to produce a note the time could be 

 brought up to 007 sec, corresponding to a velocity 

 of only 14 cm. per sec. 



With regard to the much disputed point as to 

 whether it is possible to vary the quality of the note 

 independently of the loudness, this must, I think, still 

 be regarded as an open question. Very positive 

 affirmations are made by musicians on both sides. 

 From a physical point of view the suggestion made 

 by Mr. Tobias Matthay in his work on touch seems 

 to be the only possible way to explain the effect, if 

 it exists, viz. that the quality can be spoiled by vibra- 

 tions of the hammer-shaft at the instant of striking the 

 string. In accordance with this, Mr. Matthav holds 

 that the tone is good when the final velocity is given 

 to the key gradually, and is bad when the same 

 velocity is imparted by a sudden blow. That vibra- 

 tions of the shaft occur is, of course, undoubted, but 

 whether they are sufficient to cause an appreciable 

 effeel is another matter. On the other side, recent 

 German theorists, such as Breithaupt, Steinhausen, 

 and Ritschl, denv the effect altogether. The last- 

 named author holds that good touch consists in the 

 power to produce fine gradations of intensity and 

 in complete mastery of legato and the use of the 

 pedal. 



no. 2280, VOL. 9 r~l 



The essential question seems to be whether good 

 and bad touch can be distinguished in a single note 

 struck and allowed to die away, or in a succession 

 of notes following each other at so long intervals 

 as to be musically detached. As 1 understand Prof. 

 Bryan, the improvement effected by his invention is 

 chiefly apparent in a sequence of notes forming a 

 melodic phrase. Further, 1 think that the exact 

 dynamical effect of the contrivance on the motion of 

 the key has not been made quite clear in the pub- 

 lished account. W. B. Morton. 



The Queen's University of Belfast, July 2. 



The Reflection of X-Rays by Crystals. 



It is interesting to find that an X-ray bulb having 

 a rhodium antikathode gives off a strong, sharply 

 defined (and therefore very homogeneous) beam which 

 is reflected from the (100) face of rock-salt at a 

 glancing angle of 6-2°. Its majss absorption co- 

 efficient in aluminium is 32. A second weaker beam 

 is reflected at an angle of 5-8°, and this 

 appears to complete the rhodium X-spectrum. Assum- 

 ing the correctness of my son's determination of the 

 spacing of the atoms of rock-salt (in a paper read 

 before the Royal Society on June 26), the wave- 

 length of the stronger beam is o-6i x io- s , and of 

 the weaker 0-57 xio-'. It can be calculated that 

 radiation of about this wave-length should be emitted 

 by a rhodium antikathode ; the argument is given in 

 a paper recently read before the Royal Society (see 

 abstract on p. 496 of this issue). 



Platinum and rhodium give much stronger homo- 

 geneous reflected rays than iridium, tungsten, or 

 nickel. The current produced in an ionisation 

 chamber 15 cm. long, filled with SO,, the slits being 

 3 mm. long and o-S mm. wide (Proc. Roy. Soc, 

 lxxxviii., p. 428), is so great that the leaf of a Wilson 

 electroscope races across the field of view at the 

 rate of thirty or fortv measurable divisions (three or 

 four scale divisions) in a second. The setting must 

 be exact, and the bulb should be verv soft. 



\V. H. Bragg. 



Rosehurst, Grosvenor Road, Leeds. 



Wireless Antennae. 



Prof. Fleming, in a recent letter to a contemporary 

 journal, has made a suggestion similar to that of 

 Mr. A. Lander, in Nature of July 3 (p. 451), to the 

 effect that the space wave in wireless telegraphy is 

 supplemented by some effect which travels through 

 the earth. Indeed, it would appear natural to expect 

 that, in addition to the electric disturbance which 

 must travel outwards in all directions over the con- 

 ducting surface of the earth when the electrical poten- 

 tial at any point on this surface is disturbed, the 

 passage of the electromagnetic waves through the air 

 above the earth's surface should be accompanied by 

 some form of electrical disturbance along the con- 

 ducting earth's surface beneath them. This is, how- 

 ever, a subject that, so far as I am aware, has not 

 yet been tackled by mathematical physicists, and I 

 would point out that it is well worth their attention. 



In connection with the matter, it may be of interest 

 to mention that I find that my own body, without 

 any wires or anything else, will serve as antenna for 

 the reception of signals from the Admiralty. My 

 receiving apparatus is on the ground floor of my 

 house in Chester Square, and with my ordinary aerial 

 disconnected I find I can get the Admiralty signals, 

 j faintly but quite audibly, simply by touching with 

 mv finger the terminal to which the aerial is usually 

 connected. No doubt in this rase my body does not 

 act as an aerial in the ordinary way, but merelyas a 

 capacity into which the electrical disturbance arriving 



