12 



NATURE 



[September i, 192 i 



has thus inherited the uniform slope of hair which, I 

 believe, is common to all mammals, but at some dis- 

 tant period of its evolution the abnormal horse began 

 to assume the incipient variation because its ancestors 

 were subject to friction from a collar sufficient to 

 produce it, whereas the normal horse and its ances- 

 tors were not. We may surely to-day call these pat- 

 terns "acquired characters," though their initial 

 stages were too slight to be discovered. In such an 

 inquiry as this, if we look away from the slight initial 

 ■stages and concentrate attention only on fully formed 

 ^'characters," we become bemused by this unfortunate 

 term with all its implications. How does it help our 

 A^iew of the matter to call both the normal and ab- 

 normal slope "acquired" because the horse inherits 

 the potentiality of responding thus to the stimuli of 

 friction? If we must do so, we shall have to find 

 some fresh term for the initial stages and changes of 

 structure. Would Semon's conception embodied in 

 the word " engram " not suit the case? On his hypo- 

 thesis "engrams" are transmitted after the opera- 

 tion of a sufficient number of stimuli. 



Will Sir Archdall Reid then tell us what he thinks 

 of such initial variations as the one I have chosen, 

 and what we should call them, if not "engrams"? 

 These considerations are apart from the complications 

 of inheritance introduced by bisexual reproduction and 

 its shuffling effect on variations. Walter Kidd. 



2 Suffolk Square, Cheltenham, August 19. 



The " Radiant " Spectrum. 



The title refers to an interesting optical effect ob- 

 served and described many years ago by Sir David 

 Brewster (Phil, Mag., September, 1867), which appears, 

 however, never to have been satisfactorily explained. 

 When a small brilliant source of light is viewed 

 through a prism held in front of the eye, a remark- 

 able appearance is noticed, represented roughly in the 

 accompanying diagram (Fig. i). In the continuation 

 of the spectrum of the source, but considerably beyond 

 its violet end, is seen a patch of light consisting of 



■RED 



VIOLET 



Pio. I. 



streamers radiating from a centre, as shown. A brief 

 statement on the cause of this effect, as determined 

 in an investigation made by me, may be of interest to 

 readers of Nature. 



The phenomenon is due to the diffraction of light 

 in its passage through the eye by the corneal cor- 

 puscles. Were there no prior dispersion of the light 

 by the prism, the diffraction-halo would appear to 

 consist of streamers surrounding the source and radiat- 

 ing from it directly. The effect of the dispersion on 

 the diffraction-halo is to shift its achromatic centre 

 towards the side of the shorter wave-lengths — in fact, 

 to a point lying considerably beyond the violet of the 

 spectrum of the source, exactly as observed. The 

 streamers in the halo really consist of elongated dif- 

 fraction-spectra, and the effect of the prism is to re- 

 orient them, so that they now appear to diverge from 

 the altered position of the achromatic centre. This 

 explanation of Brewster's phenomenon is strikingly 



NO. 2705, VOL. 108] 



confirmed by the fact that very similar effects may be 

 observed in the diffraction-halo due to a glass plate 

 dusted with lycopodium, when held in front of the eye 

 along with a 60° glass prism. 



C. V. Raman. 

 22 Oxford Road, Putney, S.W.15. 

 August 12. 



Remarkable July Rainfall at Blue Hill, Mass. 



In connection with the present abnormal season in 

 North-Western Europe, it may be of interest to note 

 that July, 192 1, was not only the wettest July, but also 

 the wettest month of any at Blue Hill since observa- 

 tions began thirty-six years ago. The co-ordinates 

 of the observatory are ^ = ^2° 12' 44" N., and A = 

 71° 6' 53" W. Every effort has been made to preserve 

 the integrity of the record. The total rainfall for 

 July was 261 mm. (10-43 i"-)' the normal rainfall 

 for that month being 99 mm. (3-92 in.). There were 

 eleven rainy days, and one on which a trace of rain 

 fell. 



So far as frequency is concerned, it was a normal 

 month. 



It is difficult to characterise properly the rainfall of 

 a summer month, owing to variability in the intensity 

 of thunder showers. During the past month there 

 were no remarkably heavy downpours such as distort 

 monthly totals. Also there was on the last dav of 

 June a heavy rainfall which, if allowed for, easily 

 makes the period one of maximum rainfall. By com- 

 parison with long-period records at New Bedford, 

 68 km. south (107 years), and Boston, 16 km. north 

 (103 years), it is evident that the rainfall of July, 1921, 

 is the heaviest in a century. With the exception of 

 August, 1826, when at New Bedford 475 mm. was 

 recorded, half of which, however, fell in 72 hours, the 

 past month can be regarded as the wettest period in 

 this section for more than a centurv. 



Furthermore, this section of the North Atlantic coast 

 is evidentlv in a period of maximum rainfall. At Blue 

 Hill the data are as follows (in the upper row normal 

 35-year-period rainfalls ; in lower rows the departures 

 for 1920 and 192 1) : — 



Tan. Feb. 



35 years mm. 103 loi 



1920 -20 -f 88 



1921 - 8 - I 



Mar. Apr. May. June. Jul v. 



no 94 91 80 99 



+ 25 +69 +101 +139 - 22 



-38+36 + 41 + 30 +166 



Aug. ?"ept. Or.'. Nov. Dec. Year. Year/12. 



100 104 99 96 98 1 179 98 



+ 25 -28 -42 +76 +23 162I 135 



----- - iso(?) 



Alexander McAdie. 

 Harvard University, Blue Hill Observatory, 

 Readville, Mass., August i. 



The " Philosophical Magazine." 



A LETTER which appears to have been widely cir- 

 culated has reached me from the National Union of 

 Scientific Workers virtually attacking the manage- 

 ment of the Philosophical Magazine. Will you allow 

 me, therefore, briefly to say that the referees men- 

 tioned on the title-page of that journal are frequently 

 consulted, and that their services are hot so nominal 

 as the writers of the circular suppose? 



I would add that, in mv judgment, the Philosophical 

 Magazine is wel' managed ; that a conservative atti- 

 tude towards old-established organs is wise ; and that 

 it is possible to over-organise things into lifelessness. 



Oliver Lodge. 



