498 



NATURE 



[December 15, 1921 





In Fig. 3, which shows umbra and penumbra in 

 proportion, isopleths for each multiple of 20 per cent, 

 of full illumination have been drawn. The ratio to 

 the lun^r diameter of the distance of each isopleth 

 from the edge of the umbra is given in the last line 



r-K) 



a. _ 



of the preceding table, the lunar diameter 2p being 

 taken as 904 milliradians. Fig. 2 exhibits the slow 

 variation of illumination near the inner and outer 

 edges of the penumbra which was anticipated from 

 general considerations. 



The explanation of Mr. Brooks's observations 

 appears to be that at the beginning of a lunar eclipse 



Fig. 3. — The small circles represent the moon in two positions, the 

 shaded circle the umbra thrown by the earth, and the outer- 

 most circle the edge of the penumbra. 



the range of the brightness I is from zero nearly to 

 I,. The dull region, say from I=o to 1 = ^1,, has a 

 width equal to 024 of the lunar diameter. With the 

 eclipse approaching totality, say when the width out- 

 side the umbra is one quarter of the diameter, the 



NO. 2720, VOL. 108] 



maximum illumination is only 0-21 1,, and the dull 

 strip, which in this case extends from I = o to 

 1 = ^X0-2 1 Ij, has a width 008 of a diameter. The 

 width of the dull or fuzzy region is therefore reduced 

 in the ratio 3:1. If this explanation be sound the 

 phenomenon is physiological rather than physical. 



A lunar eclipse presents another and much more 

 difficult photometric problem : the umbra is not per- 

 fectly black, and as is well known the slight illumina- 

 tion it receives is due to light refracted in passing 

 through the earth's atmosphere. It would be of in- 

 terest to compare the strength of this illumination 

 with that in the penumbra, and hence determine the 

 fraction of sunlight which passes through our atmo- 

 sphere without loss by diffraction and absorption. 



Though it is hardly relevant to the subject of 

 eclipses, it may be mentioned that a measurement of 

 equal delicacy and greater value would be that of 

 the brightness of the "old moon in the arms of the 

 new," from which measurement the mean albedo of 

 the earth could be deduced. One may even speculate 

 on the possibility of variation in this albedo being 

 detected, as the earth as seen from the moon is 

 covered mostly by land or by sea or by cloud. Such 

 knowledge would be of considerable value in the theory 

 of the economy of the earth's thermal energy. 



The new moon is observed from England after 

 sunset when the western hemisphere mostly covered 

 by water is facing the moon, whereas at the end of 

 the lunar month we see the old moon in the early 

 morning when the eastern hemisphere with the larger 

 proportion of land is opposite to the moon. Con- 

 ditions are therefore favourable for detecting the con- 

 trast in question. F. J. W. Whipple. 



Meteorological Office, South Kensington, 

 S.W.7, November 15. 



Awards to Discoverers. 



In view of the Government having enforced reduc- 

 tions in State funds available for research, It may be 

 of interest to refer to the subject of awards to dis- 

 coverers as means of effecting economy in, and in- 

 creasing incentives to, research. 



In a leading article in Nature of March 31 last on 

 "Inventions and Grants-in-Aid," special consideration 

 was given to the first Report of the Royal Commis- 

 sion on Awards to Inventors, and also my scheme for 

 the administration of grants for scientific discoveries 

 and memoranda which were submitted by me to the 

 Department of Scientific and Industrial Research. 

 The scheme and memoranda were referred to in the 

 article above mentioned in relation to rewards for 

 future inventions and discoveries. In this connection 

 I wish to direct attention to certain rulings of the 

 Commission in respect of rewards for unpatented 

 inventions and discoveries, particularly as the impres- 

 sion has been formed in certain quarters that the 

 procedure of the Commission in respect of rewards 

 for unpatented inventions might be made available in 

 regard to rewards for discoveries such as those which 

 contribute to the advancement of knowledge which it 

 is desirable In the national interest to Increase. 



The discoveries for which grants may be obtained 

 In accordance with the provisions of my scheme mav 

 be scientific or medical or surgical discoveries, anc' 

 thev may be described In an allocation or allocations 

 of grants. A fund out of which grants may be allo- 

 cated may be created by the State, or by means oj 

 donations and bequests, or both these sources ma;| 

 be made available. 



I observed In my Memorandum G that "grants rnai 

 be allocated to discoveries which are unremunerativej 



