NOTES 457 



exhibited some magnificent photographs taken by him and Mr. E. E. Cottingham 

 at Principe during the total eclipse of the sun, May 29. The main purpose of the 

 expedition was to make use of a splendid opportunity of testing whether light is 

 subject to gravitation — i.e., whether a ray of light passing near the limb of the 

 sun suffers bending. There were thirteen bright stars suitably placed. Unfortu- 

 nately at Principe, at the critical period, there were hazy clouds. Of sixteen 

 photographs taken during the five minutes available, no stars appeared on the 

 first ten. Towards the end of totality the sky cleared, and the images of five 

 stars were obtained on the remaining plates. These will not be sufficient to test 

 the effect of gravitation by comparing the positions with those in the absence of 

 the sun. Fortunately, however, the expedition to Brazil had excellent conditions, 

 and, although it is not yet possible to indicate the magnitude of the deflection, 

 Prof. Eddington is convinced that some, in the correct sense, exists. 1 On the 

 other hand, according to Father Cortie, who took part in the discussion, the fact 

 remains that in the 1917 eclipse no shift was observed in forty-three stars appear- 

 ing on the same plate. 



The Principe photographs have an additional interest, actually enhanced by 

 the intervening mist, in that they show a magnificent arched prominence in the 

 corona of the sun, 100,000 miles high, and four times as broad. 



In the Discussion on Relativity, opened by Prof. Eddington, Dr. Silberstein, 



Sir O. Lodge, and Prof. Lindeman took part. There were also related papers 



" On the Limitations of Relativity" by Mr. IV. J. Johnston and Sir J. Larmor, 



and " On the sEther and the Perihelion of Mercury," by Dr. Houstoun. It is to 



be feared that the discussion did not advance matters much. It was a pity, too, 



that the eclipse calculations were not complete ; consequently it was not possible 



to use these results as a guide to the correct theory. Few people are able to 



follow Einstein, but there is no doubt that the main difficulty arises from the 



inability of many minds to dispense with what Sir O. Lodge called "an inexorable 



progress of time, independent of particular observers." Sir J. Larmor. too, thinks 



that it is wrong to regard time as constituting a fourth dimension. " Local time " 



is still the root of the difficulty, and the objection applies equally to the classical 



relativity of 1905 and Einstein's more recent development of it. Prof. Eddington 



outlined the Einstein view. Dr. Silberstein professed himself still a relativist of 



the 1905 school, and expected negative results from the eclipse observations. He 



claimed that relativity had recently obtained splendid verification, notably in 



Somerfield's adaptation to Bohr's theory of atoms. He was, however, as much 



opposed to Einstein's theory as to the non-relativistic view. Sir O. Lodge is still 



unconvinced. He answered Prof. Eddington's objection to the pretence of 



measuring lengths although no invariable scale exists, by pointing out that we 



can and do measure absolute temperatures by means of real imperfect gases, 



although there exist no ideal ones. 



In addition to the Principe photographs there were two papers on astronomical 

 subjects : " On Nova Geminorum," by Lieut. -Col. Stratton, and " On Nova 

 Aquilce" by Father Cortie. The behaviour of these two novae — and, indeed, 

 Nova Persei also — has been, apparently, very similar, and there is evidence of 

 prodigious velocities in the materials constituting the outer layers. Shifts of 

 absorption bands equivalent to velocities of 2,400 kilometres per second have been 

 observed. 



1 By the time this report appears it h probable that the definite result will 

 have been announced, enabling us, perhaps, to decide between the non-relativistic 

 view which suggests a deflection of o'Zj", and the Einstein theory which antici- 

 pates double this amount. 



30 



