312 SIR F. W. DYSON, PROF. A. S. EDDINGTON AND MR. C. DAVIDSON ON A 



In photograph No. 15, star 10 is not shown, and the equation is slightly modified. 

 It may also be noticed that the values are somewhat smaller for Nos. 15 to 18. 

 The means of the 16 photographs treated in this manner give 



= + O r -0435, 



or with the value of the scale O r 082 from the previous table 



a = 4- O r -024 = 0"-93 at the limb. 



It may be noticed that the change of scale arising from differences of refraction and 

 aberration is O r< 020. If this value of e be taken instead of O r> 082 we obtain 



= : -f O r -039 = + l"-52 at the sun's limb. 



* 



The equations on p. 311 were also solved by least squares for each plate. There is a 

 considerable range in the deduced values of a, as is to be expected when a and e are 

 determined independently for each plate. The mean result for a is 0"-99, or very 

 nearly the same as that already found. 



The photographs taken with the astrographic telescope support those obtained by 

 the " 4-inch " to the extent that they show considerable outward deflection, but for 

 the reasons already given are of much less weight. 



IV. THE EXPEDITION TO PRINCIPE. 



* 



(Observers, Prof. A. S. EDDINGTON and Mr. E. T. COTTINGHAM.) 



26. The expedition left Liverpool on the " Anselm " on March 8, and travelled in 

 company with the Sobral expedition as far as Madeira. It was necessary to wait 

 there until April 9, when the journey was continued on the " Portugal," belonging to 

 the Companhia Nacional de Navegaao. The expedition landed at the small port of 

 S. Antonio in the Isle of Principe on April 23. 



Vice-Admiral CAMPOS RODRIGUES and Dr. F. OOM of the National Observatory, 

 Lisbon, had kindly given us introductions, and everything possible was done by those 

 on the island for the success of the work and the comfort of the observers. We were 

 met on board by the Acting Administrator Sr. VASCONCELOS, Sr. CARNEIRO, President 

 of the Association of Planters, and Sr. GRAGEIRA, representing the Sociedade d'Agricul- 

 tura Colonial, who made- all necessary arrangements. The Portuguese Government 

 dispensed with any customs examination of the baggage. 



27. Principe is a small island belonging to Portugal, situated just north of the 

 equator in the Gulf of Guinea, about 120 miles from the African coast. The extreme 

 length and breadth are about 10 miles and 6 miles. Near the centre mountains rise 

 to a height of 2500 feet, which generally attract heavy masses of cloud. Except for 

 a certain amount of virgin forest, the island is covered with cocoa plantations. The 



