Item 3 - Account of an expedition to Principe

2 single sheets

(This is an early version of part of a report to the Royal Society by the Joint Permanent Eclipse Committee. The latest date mentioned in it is 14 July 1919, and the report was received by the Society on 30 October and read on 6 November.)

Printed in a revised form as the first part of Section IV (pp. 312–14), in Sir F. W. Dyson, A. S. Eddington, and C. Davidson, ‘A Determination of the Deflection of Light by the Sun’s Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919’ (Philosophical Transactions of the Royal Society of London, series A, vol. ccxx (June 1920), pp. 291–333).

TRANSCRIPT:

The observers, Prof. A. S. Eddington and Mr E. T. Cottingham travelled in company with the Sobral expedition as far as Madeira which was reached on March 14. They left Madeira on April 9 by the Portugal, a steamer belonging to the Companhia Nacional de Navegaçaõ†, and reached Principe on April 23.

Through the kindness of Vice-Admiral Campos Rodrigues and Dr Oom of the Lisbon Observatory arrangements had been made for the reception of the expedition. The Acting Administrator Sr. Vasconcélos, Sr. Carneiro, and Sr. Grageira representing the Sociedade Agricultura Colonial met them on board and offered every facility.

Principe is a small island about 10 miles long by 6 miles wide, lying just north of the equator about [blank] miles from the west coast of Africa. Near the centre mountains rise to a height of 2500 feet and are generally covered with cloud; the rest of the island is almost entirely given up to the cultivation of cocoa. We arrived near the end of the rainy season, and a different type of weather was due to set in about the middle of May[.] We were advised that the prospects of a clear sky at the end of May were not very good, but that the best chance was in the North and West of the island. Two sites were inspected on the property of the Sociedade Agricultura Colonial; but it was found that Roça Sundy, the headquarters of Sr Carneiro’s chief plantation was the most suitable in every way. We were Sr. Carneiro’s guests during our whole visit, either at his house in the port of S. Antonio or at Roça Sundy and we are greatly indebted to him and to his manager at Sundy, Sr. Atalaya, both for our personal comfort and for their general assistance. We were able to draw freely on the ample resources of the Roça in erected† the instruments.

The baggage was transported from S. Antonio to Sundy, April 28, and we went over the same day. After a week’s work, we had made as much progress as possible without unpacking the coelostat-mirror; as we were unwilling to expose this for so long to the tarnishing effect of the damp climate, we returned to S. Antonio for the week May 6–13.

On returning to Sundy, the installation and adjustments were soon completed and the first check plates were taken on May 16. Meanwhile, the Gravana or dry season had begun. Except on the day of the eclipse no more rain fell during our visit. The cloud, however, was more persistent though there were some clear days. The nights were generally clear.

The days preceding the eclipse were almost completely overcast. On the morning of the 29th there was a heavy thunderstorm from about 10–11∙30. The sun then appeared for a few minutes, but the clouds soon gathered again. The sun was invisible at first contact. About half-an-hour before totality the crescent sun was glimpsed occasionally and by 1h ∙55m it could be seen continuously through the driving cloud. The calculated time of totality was from 2h 13m 5s to 2h 18m 7s and the exposures were made according to the prepared programme. 16 plates were obtained. It appears from the results that the cloud must have thinned considerably during the last third of totality. A few minutes after totality the sun was in a perfectly clear sky but after a short time the sky became overcast again. It seems likely that the partial clearance was caused by the eclipse, and was similar to the clearance which usually occurred after sunset.

It had been intended to complete the measurement of the plates on the spot, but owing to a strike of the Steamship Company it was essential to return by the next boat if wer were not to be marooned on the island for some months. By the intervention of the Administrator, berths were recured for us on the crowded steamer. We left Principe on June 12, and after transhipping at Lisbon reached Liverpool on July 14.