RECENT ADVANCES IN SCIENCE $33 



photographing the integrated light of the sun reflected by- 

 Venus. A series of photographs was obtained when the angle 

 at the sun was approximately 45°, 75 , 95 and 135 , and 

 the surprising result was found that there was a progressive 

 diminution of wave-length of the solar iron lines as Venus 

 passed towards superior conjunction. With some lines a shift 

 towards the violet was found in certain positions. It is there- 

 fore evident that the shift towards red of the solar lines only 

 occurs on the side of the sun facing the earth, whereas a gravi- 

 tational effect would be constant all over the sun. Not a single 

 plate gave a contrary result. The displacements obtained ap- 

 pear therefore to be due to a recessive motion of the solar 

 gases controlled by the earth, the cause of which is, however, 

 at present obscure. There seems to be therefore no escape 

 from the conclusion that the prediction from theory of a 

 gravitational displacement of the solar spectrum lines is not 

 verified. 



It may be mentioned that in order to make accurate measure- 

 ments of small displacements of the solar lines, Mr. Evershed 

 devised a special method of measurement in which a positive 

 spectrum is superposed on a negative and the double displace- 

 ment measured. The method is described in the Observatory, 

 11, 275 and 443, 191 8. 



It is possible that the remaining prediction of the theory 

 which is susceptible of testing may soon be verified or disproved, 

 rhe theory requires a displacement of the rays from a star by 

 ;he gravitational field of the sun. The only possibility of testing 

 ;his conclusion at present is by photographing the sun and the 

 leighbouring stars during a total eclipse. In general, how- 

 ever, at the time of totality, the sun does not happen to be in 

 1 region of the sky containing sufficiently bright stars. At 

 ;he forthcoming eclipse of 1919, May 29, however, the sun is 

 /ery favourably situated on the Hyades and a unique oppor- 

 .unity is provided of testing the theory. Two expeditions 

 lave left this country under the auspices of the Joint Per- 

 nanent Eclipse Committee of the Royal and Royal Astrono- 

 nical Societies, one of which has gone to the island of Principe 

 )ff the West Coast of Africa, whilst the othter has gone to Brazil. 

 Standard astrographic objectives of 13-inch aperture are being 

 ised, and the eclipse photographs will be compared with 

 Photographs of the same field obtained at night during last 



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