May I, 19 19] 



NATURE 



165 



about 1700, but growing for market purposes was 



not seriously taken up for another century, after 

 which the need for improved varieties soon arose. 

 A new era was ushered in in 1834 by the intro- 

 duction of the Hovey strawberry, which was the 

 first named variety to be produced by definite 

 plant breeding in North America. From this time 

 the development of commercial cultivation was 

 rapid, and it was accentuated by the competition 

 due to increased facilities for transporting the 

 fragile berries over longer distances. The tender- 

 ness of the fruit necessitated a search for the ideal 

 package for marketing, and many descriptions of 

 punnets, boxes, tubs, and trays have been ex- 

 ploited. 



The survey includes an outline of observations 

 and experiments on the crossing of species and 

 the raising of new varieties. The illustrated 

 account of present-day methods of breeding and 

 selection gives a useful summary of the subject, 

 and the sketches of abnormal freak berries are 

 of interest to the morphologist. The. biographical 

 notices in the last chapter form a fitting con- 

 clusion to the book by directing attention to the 

 men to whose careful and patient work is due the 

 great improvement in the strawberry in North 

 America. 



The Journal of the Itistitute of Metals. No. 2. 

 19 1 8. Vol. XX. Edited by G. Shaw Scott, 

 secretary. Pp. xi + 382. (London: Published 

 by the Institute of Metals, 1918.) Price 21s. 

 net. 

 The twentieth volume of this valuable publication 

 contains a variety of papers of scientific and tech- 

 nical interest. The May lecture, by Sir Charles 

 Parsons, describes the experiments on the arti- 

 ficial production of diamond made by the lecturer 

 during the last thirty years, and discusses the 

 bearing of the results obtained on the problem 

 of the origin of natural diamonds. A group of 

 papers deals with the grain growth of metals,^ 

 Dr. Zay Jeffries giving a review of the whole 

 subject,' and making much use of experiments 

 with tungsten filaments. The observations are by 

 no means easy to interpret, and some of the con- 

 clusions appear to contradict one another; but 

 the author has made a most important contribu- 

 tion to a subject of great interest, and it may be 

 possible shortly to bring the facts into harmony. 

 Mr. D. Hanson, in a short note, describes experi- 

 ments on the same problem, discussing the rela- 

 tion between the rapidity of grain growth at a 

 given temperature and the amount of deformation 

 to which the material has been previously sub- 

 jected. 



A third paper, by Mr. R. J. Anderson, 

 describes the effect of short exposures to various 

 temperatures on cold-rolled aluminium sheet, and 

 although it is the hardness in this case, and not 

 the grain size, which is measured, the phenomena 

 involved are essentially similar to those discussed 

 in the preceding papers. Prof. Edwards gives an 

 account of the method of determining hardness by 

 measuring the resistance to penetration under im- 

 NO. 2583, VOL. TO3] 



pact, and there are several contributions on the 

 subject of commercial copper alloys. An interest- 

 ing communication by Mr. W. E. Alkins records 

 the effect of progressive cold work on the tensile 

 properties of copper wire, an abrupt change being 

 observed at a certain stage in the reduction of 

 cross-section by drawing. The allotropic change 

 assumed by the author requires more evidence 

 before it can be accepted as an explanation, but 

 the facts are remarkable, and must be taken into 

 account in future work. The volume includes the 

 usual abstracts of publications referring to the 

 non-ferrous metals. C. H. D. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The Doppler Effect in the Molecular Scattering of 

 Radiation. 



In connection with the recent work of Prof. Strutt 

 and of Lord Rayleigh on the molecular scattering of 

 light. Sir Joseph Larmor has put forward the interest- 

 ing suggestion {Phil. Mag., January, 1919, p. 162) 

 that the additive property of the energy elements scat- 

 tered by the individual molecules is secured by the 

 irregular alterations in the wave-length of the scat- 

 tered radiation produced (in accordance with Doppler's 

 principle) by the thermal movements of the mole- 

 cules. There is one interesting feature of the Doppler 

 effect in the scattered radiation to which Sir Joseph 

 Larmor does not specifically direct attention in his 

 paper, and which it seems important to emphasise, 

 namely, that the magnitude of the Doppler effect 

 would depend on the angle between the primary and 

 the scattered radiation, and would, in fact, practically 

 vanish in directions nearly the same as that of the 

 primary waves. This follows from the fact that the 

 movement of an individual molecule would alter the 

 effective frequency of the radiation received by it, and 

 this has to be taken into account in calculating the 

 effective frequency of the emitted radiation as re- 

 ceived bv the observer. In directions nearly the same 

 as that of the primary radiation there would be prac- 

 tically a complete compensation, and the Doppler effect 

 would vanish. 



The importance of the considerations set out above 

 becomes evident when we attempt to explain refrac- 

 tivitv on the basis of molecular scattering. This 

 appears possible onlv if the energy effects due to the 

 individual molecules are not additive in directions 

 nearly the same as that of the primary wave, and the 

 vanishing of the Doppler effect in the scattered radia- 

 tion would seem to be a necessary condition for 

 mutual interference of the radiations from individual 

 molecules to be possible. C. V. Raman. 



210 Bowbazar Street, Calcutta, March 19. 



TnK point developed in a new direction by Prof. 

 Raman had been noted by Lord Rayleigh, and was 

 mentioned verv cursorily in the last sentence of my 

 paper in the Phil. Mag. to which his letter refers. 

 The main purpose of that paper was to express the 

 view that, so far as I understand, independent scat- 

 tering of light bv the molecules of a homogeneous 



