November 13, 1919] 



NATURE 



28j 



a suitable equatorial mounting, though it is hoped ' 

 that this may be done before the eclipse of 1922. 



The results, to some extent, but, fortunately, 

 not entirely, justified these apprehensions. The 

 eclipse plates taken with the 13-in. (stopped down 

 to 8 in.) are out of focus. Since the focus was ; 

 good on photographs taken at night a few hours 

 earlier, and also on the check plates taken before 

 sunrise in July, the explanation appears to be a 

 change of figure of the coelostat mirror, due to 

 the heat of the sun. These plates were compared 

 with the July check plates by using a duplex 

 micrometer. They show an undoubted gravita- 

 tional shift, the amount at the sun's limb being 

 o'93" or o'99", according to two different 

 methods of treatment. The probable error, as esti- 

 mated by the individual discordances, is about 

 o'3", but there is reason to suspect systematic 

 error, owing to the very different character of the 

 star-images on the eclipse and check plates. This 

 instrument supports the Newtonian shift, the 

 amount of which is o'Sy" at the limb. There is 

 one mode of treatment by which the result comes 

 out in better accord with those of the other instru- 

 ments. Making the assumption that the bad focus 

 did not alter the scale, and deducing this from ' 

 the July plates, the value of the shift becomes 

 i-52'/. 



The results with the 4-in. lens are much more 

 satisfactory. The star-images are well defined, 

 and their character is the same on the eclipse and 

 check plates. As the duplex micrometer would 

 not fit these plates, a key-plate, on which the 

 film was placed away from the lens, was taken 

 in July, and all the plates in turn were placed in 

 contact with this plate and compared with it. The [ 

 resulting shift at the limb is i'98", with a prob- : 

 able error of 012". The values from the separate ' 

 stars are in good accord, and they support the 

 fact of the shift varying inversely as the distance 

 from the sun's centre; thev are thus unfavourable 

 to its being due to refraction, as was suggested 

 by Prof. Newall at the meeting. Moreover, Prof. 

 Lindemann pointed out that the comets of 1880 

 and 1882 had traversed this region without giving 

 the slightest evidence of having encountered re- 

 sistance; as their speed was about 300 miles per I 

 second, a vivid idea is given of the extreme j 

 tenuity of anv medium that they encountered. ' 



The Principe expedition was less fortunate in 

 the matter of weather, but a few plates showed 1 

 five stars. Since no check plates of the eclipse 

 field could be taken there, another field near ' 

 Arcturus was photographed, and both it and the 

 eclipse plates were compared with p'ates of the 

 same fields taken at Oxford with the same object- 

 glass. It was, moreover, necessary to assume 

 that the scale of the eclipse plates was the same 

 as that of the check plate. This is justified by 

 the fact that the diurnal variation of temperature 

 in Principe is only some 4° F., and that there 

 had been no bright sunshine on the mirror before 

 totality. The measures indicate a shift at the 

 limb of i'6o", with a probable error of o'3". 



It will be seen that the mean of this result and 

 NO. 261 I, VOL. 104] 



that with the 4-in. at Sobral agrees very closely 

 with Einstein's predicted value 175". It was 

 generally acknowledged at the meeting that this 

 agreement, combined with the explanation of the 

 motion of the perihelion of Mercury, went far to 

 establish his theory as an objective reality. Sir 

 J. J. Thomson, who presided, spoke of the veri- 

 fication as epoch-making; he suggested that it 

 would probably have a bearing on electrical 

 theory, but he regretted the very complicated 

 form in which Einstein expressed his theory, and 

 hoped that it might be possible to put it into a 

 form in which it would be more generally com- 

 prehensible and useful. 



Dr. Silberstein laid great stress on the failure 

 lo confirm Einstein's third prediction, that of the 

 displacement of lines in the sun's spectrum to- 

 wards the red, to the amount of 1/20 Angstrom 

 unit ; this had not been verified, in spite of the 

 careful search made by Dr. St. John and Mr. 

 Evershed. As the probable error of their measures 

 was much less than the quantity predicted, he 

 looked on this result as final ; some people had 

 suggested that the shift might be veiled by a 

 systematic outward movement of the photosphere, 

 but. as Dr. St. John made measures both at the 

 sun's centre and limbs, that suggestion was not 

 tenable. Prof. Eddington admitted that the failure 

 threw doubt on the validity of some of the steps 

 which led Einstein to his gravitational result ; but 

 he contended that the two other successes indi- 

 cated that the result was right, even if reached 

 by a wrong method. 



There was some discussion on Prof. Linde- 

 mann 's method of photographing stars in daylight 

 by the use of red screens. However, the eclipse 

 method seems more trustworthy, and the Astro- 

 nomer Royal expressed the hope that the eclipse 

 of 1922 might be observed with equatorials. The 

 star-field is not so rich as in the late eclipse, but 

 with longer exposure much fainter stars could 

 be recorded. The eclipse-track crosses the 

 Maldive Islands and .Vustralia, and is therefore 

 fairlv accessible. A. C. D. Crommelin. 



THE JUBILEE OF "NATURE": CON- 

 GRA TU LATOR Y M ESS A GES. 



TT is with a certain amount of diffidence that we 

 give here a number of cordial messages which 

 have reached us upon the attainment of the 

 fiftieth anniversary of the foundation of Nature. 

 We believe, however, that many readers will be 

 interested not only in the friendly greetings ex- 

 pressed in these messages, but also in the refer- 

 ences to the work of science, and its expanding 

 field of usefulness. To the official representatives 

 of scientific societies and university institutions, 

 and to the other men of light and leading who 

 have honoured us with their congratulations, we 

 offer our sincerest thanks. Such pppreciation of 

 past efforts affords the strongest st-mulus to 

 future endeavour. 



While Natirf. has the advantage of the active 



