NATURE 



[September 2, 1920 



Letters to the Editor. 



(Th« Editor iocs not hold himself responsible lor opinions 

 expressed by his correspondents. Neither can he undertake to 

 return, or to correspond with the tvrilers ol, rejected manu- 

 scripts intended tor this or any other part of Naturb. No 

 notice is taken ol anonymous communications.! 



Colour of the Night Sky. 



So far as 1 have been able to learn, little or nothing 

 is known about the colour of the night sky. The 

 light is too faint for ordinary visual discrimination of 

 colour, which disappears with diminishing intensity of 

 illumination much before the light itselt ceases to be 

 perceptible. 



1 have obtained evidence, both visual and photo- 

 graphic, that the clear sky at night is much yellower 

 or less blue than the clear, or even the cloudy, sky at 

 twilight. 



The visual observations were made in the following 

 way : — Two gelatine films were prepared, one dyed 

 yellow with Havazine and the other with methylene- 

 blue, the relative intensities being adjusted by trial to 

 give the effects that will presently be described. The 

 films were mounted edge to edge at the end of a paste- 

 board tube, which was pointed at the sky. During the 

 daytime the yellow film was confidently pronounced 

 by all observers to be the brightest, the difference being 

 too marked to be embarrassed by colour difference. 

 As twilight advanced the Purkinje phenomenon came 

 into evidence, and the blue film became much the 

 brighter. This remained the case when the light had 

 waned so far that the colour sensation had dis- 

 appeared. As the stars came out the predominance 

 of the blue became less marked, and before the Milky 

 Way was distinguished there was equality. Finally, 

 when the Milky Way was conspicuous the yellow film 

 was notably the brighter, whether the tube was 

 pointed to the Milky Way or to other parts of the sky. 



The changes described were very marked. Their 

 general course was the same whether the sky was 

 clear or cloudy at any particular stage. The first 

 change, when blue becomes predominant, is due 

 solelv to phvsiological causes. But the second change, 

 which makes the yellow predominant again, occurs 

 below the " threshold " of colour-vision, and, according 

 to received views, there should be no marked com- 

 plication from phvsiological causes within this range. 

 Accordingly we may conclude that the observation 

 affords definite evidence that the night sky is yellower 

 or less blue than the day sky. 



This conclusion has been confirmed photographically. 

 A yellow and a dense blue filter were selected, and an 

 Ilford panchromatic plate was exposed to the sky 

 under these. It was seen at a glance that the density 

 under the blue filter was the greater for the twilight 

 skv, while for the night sky this relation was reversed. 



The results point to the conclusion that the light of 

 the night skv, whatever the cause of it may be, i.s 

 not due to the scattering of sunlight by rarefied gas 

 situated beyond the earth's shadow. The comparative 

 absence of polarisation, formerly found, points to the 

 same conclusion. . Rayleich. 



Beaufront Castle, Hexham, .August 20. 



University Grants. 



The article and letters in Natiire upon the subject 

 of universitv finance are very timely. It is essential 

 that the country should be alive to the perilous condi- 

 tion of the universities from a financial point of view. 



The raising of fees that has just taken place can 

 be onlv a partial remedy. Fee revenue before the 

 war provided at the various universities at the most 

 for 40 per cent, of the necessary expenditure, the 

 average being about 33 per cent. The recent increase 



NO. 2653, VOL. 106] 



in fees will barely re-establish the .pre-war per- 

 centage. 

 I agree with the Principal of Birmingham University 



that the stipends of the non-professorial staffs must 

 be increased ; the urgency is not less great for the 

 salaries of the professorial staffs. In London the 

 utmost that has been done for the professorial staff is 

 to increase the minimum full-time salary from 6ooi. 

 to Soo/. 



Now the majority of the London professors receive 

 the minimum. Considering the responsibilities of a 

 university professor, what is 800I. a year for a man 

 in that position under present conditions? Such a 

 prosf>ect will not induce young men of the right calibre 

 to make university teaching their profession. 



It is true that the Government has made non- 

 recurring grants to pay off war losses, and for 

 the time being doubled the grants. Having regard 

 to the condition of the National Exchequer, the 

 Government has perhaps done as much as could be 

 expected for the current year. The all-important 

 question for the universities is : What is the Govern- 

 ment going to do next year? 



It must be remembered that the maintenance grants 

 are made for periods of five years, and are then 

 revised. Revision was due in 1915, but was impossible 

 during the war. The period 1910-15 had been one of 

 unusual activity and development in all the universi- 

 ties. It was the general expectation in 1914 that the 

 grant for the quinquennium 1910-15 would be 

 doubled for the period 1915-20. By doubling the 

 1910-15 grant now the Government has done no 

 more than redress the disadvantage due to the 

 depreciation in the value of money. 



Having that in mind, the deputation of Vice- 

 Chancellors and Principals in 19 19 impressed on the 

 President of the Board of Education and the Chan- 

 cellor of the Exchequer that the smallest grant that 

 would meet the needs of the moment would be the 

 1910-15 grant quadrupled. That will do no more than 

 enable the universities to carry on; it will not pro- 

 vide the capital necessary for new buildings, new- 

 plant, and equipment, nor will it enable justice to 

 be done to the older men who bore the heat and 

 burden of the day of pioneer work before the time 

 of the establishment of superannuation funds. 



There are manv such men due to retire in the next 

 few years ; thev are entitled to treatment at least 

 as generous as that given to schoolmasters by the 

 Fisher Act. Gregory Foster. 



University of London, University College, 

 -August 23. 



The only elements of our society which seem to bene- 

 fit from the great increase in the wealth of the world 

 through science are those which it will be one of the 

 hardest problems of reconstruction to divert into more 

 productive and honourable means of livelihood. Those 

 who sow the seed and reap the harvest alike, year by 

 vear, bv their labours seem to be able only to increase 

 their dependence upon private charity and public doles. 

 Universities sow the seed, and their claims, like the 

 claims of the farmer for seed for his future harvest, 

 ought to be absolutely the first charge upon the yearly 

 revenue. It is as idle to sav the country cannot afford 

 it as it would be for a farmer to grudge the seed for 

 his next year's crop. It affords a plethora of most 

 expensive evils and unnecessary luxuries. In the spirit 

 of one of the earlv Methodist preachers, I feel, when- 

 ever I see a specially sumptuous motor-car, "There, 

 but for the grace of Parliament, goes a professor of 

 chemistry"; and even a humble two-seater might in 

 hanpier circumstances have become a demonstrator ! 



Under the scheme of a professor of literature with 

 fifteen years' experience of fostering scientific research 



