332 SIR F. W. DYSON, PEOF. A. S. EDDINGTON AND MR. C. DAVIDSON ON A 



Thus the results of the expeditions to Sobral and Principe can leave little doubt that 

 a deflection of light takes place in the neighbourhood of the sun and that it is of the 

 amount demanded by EINSTEIN'S generalised theory of relativity, as attributable to 

 the sun's gravitational field. But the observation is of such interest that it will 

 probably be considered desirable to repeat it at future eclipses. The unusually 

 favourable conditions of the 1919 eclipse will not recur, and it will be necessary to 

 photograph fainter stars, and these will probably be at a greater distance from the sun. 



z 



LJ 



2 



Ld 

 O 



a 

 5 



_i 

 < 



Q 



o-o 



DISTANCE 



r 



90 60 50 



Diagram 2. 



40 



This can be done with such telescopes as the astrographic with the object-glass stopped 

 down to 8 inches, if photographs of the same high quality are obtained as in regular 

 stellar work. It will probably be best to discard the use of ccelostat mirrors. These 

 are of great convenience for photographs of the corona and spectroscopic observations, 

 but for work of precision of the high order required, it is undesirable to introduce 

 complications, which can be avoided, into the optical train. It would seem that some 

 form of equatorial mounting (such as that employed in the Eclipse Expeditions of the 

 Lick Observatory) is desirable. 



In conclusion, it is a pleasure to record the great assistance given to the Expeditions 

 from many quarters. Reference has been made in the course of the paper to some 

 of these. Especial thanks are due to the Brazilian Government for the hospitality 

 and facilities accorded to the observers in Sobral. They were made guests of the 



