156 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
In photograph No. 15, star 10 is not shown, and the equation is 
slightly modified. It may also be noticed that the values are some- 
what smaller for Nos. 15 to 18. 
The means of the 16 photographs treated in this manner give 
a+243e=-+0.0435", 
or with the value of the scale 0.082" from the previous table 
a=-+0.024"=0.93’" at the limb. 
It may be noticed that the change of scale arising from differences 
of refraction and aberration is 0.020". If this value of e be taken 
instead of 0.082" we obtain 
a—=-+0.039T=+1.52”" at the sun’s limb. 
The equations on page 155 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 « and e are determined independently for each 
plate. The mean result for « 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 con- 
siderable 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. EH. T. Cottingham. ] 
26. The expedition left Liverpool on the Anselm on March 8, and 
traveled 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 
Navegacio. ‘The expedition landed at the small port of San 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 every- 
thing 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. Vasconcélos, Sr. Carneiro, president of 
the Association of Planters, and Sr. Grageira, representing the 
Sociedade d’Agricultura Colonial, who made all necessary arrange-_ 
ments. 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 center mountains rise to a height of 
2,500 feet, which generally attract heavy masses of cloud. Except 
