332 SIR F. W. DYSON, PROF. A. S. EDDINGTON AND ^IR. 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 vdll 
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. 
n 
This can be done with such telescopes as the astrographic vdth the object-glass stopped 
down to 8 inches, if photographs of the same high quality are obtained as in regidar 
stellar work. It will probably be best to discard the use of coelostat 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 woidcl seem that some 
form of ecpiatorial 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 
