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



9'iThe residuals* in the separate comparisons reduced to arc are as follows. They do 

 not appear to show any special peculiarities. 



The average ^/-residual is 0"'22, which gives a probable error for y of 0"-21. 

 It is satisfactory that this agrees so nearly with the probable error (0"-22) of the 

 check plates, showing that the images are of about the same degree of difficulty and 

 therefore presumably comparable. The probable error of x is 0"-25, but we are 

 not so much concerned with this. 



The weight of the determination of SK is about 3 (strictly 3-23 for Plate X and 2-87 

 for Plate W). The probable error of K is therefore 0"-12, which corresponds to a 

 probable error of 0"-38 in the final values of the deflection. 



As the four determinations involve only two eclipse plates and are not wholly 

 independent, and further small accidental errois may arise through inaccurate 

 determination of the orientation, the probable error of our mean result will be 

 about 0"-25. There is further the error of 0"-14 affecting all four results 

 equally, arising from the determination of scale. Taking this into account, and 

 including the small correction 0"-04 previously mentioned, our result may be 

 written 



1"-610"-30. 



It will be seen that the error deduced in this way from the residuals is considerably 

 larger than at first seemed likely from the accordance of the four results. Nevertheless 

 the accuracy seems sufficient to give a fairly trustworthy confirmation of EINSTEIN'S 

 theory, and to render the half-deflection at least very improbable. 



38. It remains to consider the question of systematic error. The results obtained 

 with a similar instrument at Sobral are considered to be largely vitiated by systematic 



* The residuals refer to the theoretical deflection l"-75, not the deduced deflections. 



