September 29, 1923] 



NATURE 



471 



for the purpose. Since 191 4 the work has been under 

 the control of Dr. P. S. Hunter, now Health Officer 

 of Singapore. He has extended the area greatly ; 

 to him the success of the work is mainly due. Dr. 



» Hunter has also extended the work to the fortified 

 island of Blakan Mati, with great advantage to the 

 garrison. Indeed Singapore has now ceased to be 

 malarial, so far as the troops are concerned. The 

 area under mosquito control is almost six square 

 miles. There are 8f miles of concrete channels and 



= t3 -• 



c JV 



Fig. I. — Death-rates of city of Singapore. 



Average 1Q03-1912 • < • 



Average 1913-1922 • — • — • 



^31 miles of subsoil drainage. A sum of approximately 

 [350,000 dollars (say 38,000/. sterling) has been spent on 

 [capital and maintenance accounts. This year there 

 [is a vote of 100,000 dollars (say 12,000/.) for mainten- 

 [ance and extension of anti-malarial and general anti- 

 I mosquito work. 



Further details will be found in the chapter on the 

 i" Malaria of Singapore," which Dr. Hunter con- 

 [tributed to my " Prevention of Malaria in the 

 [Federated Malay States" (London: John Murray, 

 (I921) : see also Nature, March 16, 1922, p. 334. 

 [Following the anti-malarial work, the spleen rate of 

 [the children fell progressively from about 50 to zero. 

 SThe great malarial wave, which raised the death-rate 

 [in the month of July 191 1 to 85-83 per mille, has been 

 'so flattened that the influenza peak of 1918 is now 

 responsible for the highest point. The wave will not 

 entirely disappear until the work in Singapore is com- 

 pleted, and until the surrounding country ceases to 

 dump its sick on the city. Anti-malarial work is 

 : being extended into the rural districts by Dr. Scharff . 

 The peak of the malarial wave in May averaged 



for the 10 years 1903 to 191 2 



,, 1913 to 192.: 



a reduction of ... . 



I>er mille. 

 53-76 

 37-27 

 16-49 



NO. 2813, VOL. I 12] 



The average annual death-rate from all causes was^ 



per mille. 

 for the 10 years 1903 to 1912 . . 44-11 

 1913 to 1922 . . 33-73 

 a reduction of 10-38 



The average population 19 13 to 



1922 was 312,763 



The saving of life is therefore . . 32,214 



The saving of life is from all medical and sanitary 

 measures, but the most important is the control of 

 mosquitoes. 



Finally, I may add that in the 25 years since Sir 

 Ronald Ross's discovery, more than 100,000 lives have 

 been saved in Malaya alone, owing to that discovery ; 

 and the work is just beginning. 



The Far Eastern Association of Tropical Medicine 

 meets in Singapore this year. Arrangements have 

 been made to show members over the anti-malarial 

 work in Singapore, and an excursion to Carey Island 

 has been arranged. Malcolm Watson. 



Klang, Federated Malay States, 

 June 24. 



Some Consequences of the Gravitational Deflexion 

 of Light. 



The results of the eclipse expeditions of 1919 and 

 1922 leave little doubt that the deflexion of i-ys" 

 predicted by Einstein for a ray of light passing close 

 by the sun is a fact. Moreover, as a result of the 

 experiments of Lebedew and Poynting, it is ad- 

 mitted generally that such a ray possesses momentum 

 as well as energy. It does not appear to have been 

 noticed that these experimental results lead to 

 certain important consequences when they are 

 combined with the generally admitted principles of 

 conservation of momentum and of energy. 



Let us suppose for the sake of argument that the 

 energy of the ray of light, and consequently also the 

 ■magnitude of its momentum, remains unaltered in 

 spite of the deflexion. Since the direction of the 

 momentum has been changed, its component along 

 the real axis of the approximately hyperbolic path 

 has been reversed ; if we retain the principle of 

 conservation of momentum for the system sun-light- 

 ray, we conclude that the sun has acquired momentum 

 along the real axis and therefore kinetic energy also. 

 According to the principle of conservation of energy, 

 the energy of the light-ray must have diminished by 

 an equal amount — a conclusion which contradicts 

 the original assumption. Thus we are led to a 

 dilemma : either we must reject one or other of the 

 two principles of conservation of momentum and of 

 energy for the action between the light-ray and the 

 sun, or we must admit that the energy of the light- 

 ray has diminished, as well as its momentum. 



It is difficult to imagine a mechanism by which the 

 energy lost by the light-ray is transferred to the sun 

 on the wave theory, though no doubt the pressure 

 of light will play the predominant part, but it is 

 obvious according to the quantum theory. Without 

 entering into details, which must be reserved for a 

 future paper, I may be allowed to refer to one im- 

 portant consequence of the assumption that the light- 

 ray loses part of its energy, namely, that its wave- 

 length is increased by a small amount. 



In fact, if the deflexion be S, the light quantum 

 makes the angle (t-8)/2 with the major axis 

 initially and finally on opposite sides of it. Con- 

 sequently its loss of momentum in that direction is 

 (2vhlc) cos (ir -S)l2, or (21-/1 /c) sin 5/2 with the usual 

 notation, and this is also the gain of momentum 

 of the sun. Hence the energy transferred is equal 

 to {2v*h*lc*m) sin* 5/2, where m is the mass of the 



