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



was made for the focussing and squaring on of the plates. The plate holders were of a 

 simple construction, permitting the plate to be pushed into contact with three metal 

 tilting screws on the breech piece thus insuring a constancy of focal plane. Eighteen 

 plate-carriers were obtained for each of the astrographic telescopes, made according 

 to a pattern supplied. 



With the 4-inch lens Father CORTIE lent the square wooden tube used by him in 1914. 

 This was modified at the breech end to secure greater rigidity and constancy of focus. 



It was designed for dark slides carrying 10 X 8 inch plates, and four of these, carrying 

 eight plates, were lent with the telescope. The desirability of using larger plates was 

 considered, but the time at disposal to make the necessary alterations was insufficient. 



The 16-inch coelostats which had been overhauled by Mr. COTTINGHAM were mounted 

 and tested as far as the unfavourable weather conditions of February, 1919, would permit. 

 The 8-inch coelostat was constructed for these latitudes. To make it serviceable near 

 the equator a strong wooden wedge was made on which the coelostat was bolted. 



The 8-inch mirror was silvered at the observatory, but owing to lack of facilities for 

 maintaining a uniform, temperature approaching 60 F. in the wintry weather of February, 

 the larger mirrors were sent away to be silvered. 



Photographic plates, suitably packed in hermetically sealed tin boxes, were obtained 

 from the Ilford and Imperial Companies. The Ilford plates employed were Special 

 Rapid and Empress, and those of the Imperial Company, Special Sensitive, Sovereign 

 and Ordinary. 



The instruments were carefully packed and sent to Liverpool a week in advance, 

 with the exception of the objectives. These were packed in cases inside hampers and 

 remained under the personal care of the observers, who embarked on the " Anselm " on 

 March 8. 



III. THE EXPEDITION TO SOBRAL. 

 (Observers, Dr. A. C. D. CROMMELIN and Mr. C. DAVIDSON.) 



9. Sobral is the second town of the State of Ceara, in the north of Brazil. Its 

 geographical co-ordinates are : longitude 2h. 47m. 25s. west ; latitude 3 41' 33" south; 

 altitude 230 feet. Its climate is dry and though hot not unhealthy. 



The expedition reached Para on the " Anselm " on March 23. There was a choice 

 of proceeding immediately to Sobral or waiting for some weeks. It was considered 

 undesirable to go there before we heard from Dr. MORIZE what arrangements were 

 being made, so we reported our arrival to him by telegram and decided to await his 

 reply. As we had thus some time on our hands we continued the voyage to Manaos 

 in the " Anselm," returning to Para on April 8. 



By the courtesy of the Brazilian Government our heavy baggage was passed through 

 the customs without examination and we continued our journey to Sobral, leaving 

 Para on April 24 by the steamer " Fortaleza " and arriving at Camocim on April 29. 



