158 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
of different declination settings, and was marked with an approxi- 
mate declination scale. A series of exposures of one second was 
made on a bright star to test whether there was any shake of the 
telescope after inserting the plate ; no shake was detected even when 
the exposure was made immediately; but as a safeguard for the 
eclipse photographs a full second was allowed to elapse before be- 
ginning the exposure. The exposure was made by moving a card- 
board screen unconnected with the instrument. The telescope pointed 
slightly downward, and the tube was turned so as to give the right 
orientation to the plate, the lines of declination being 2° or 3° in- 
clined to the horizontal. A canvas screen was arranged to protect 
the tube and object glass from the direct radiation of the sun. 
The adjustments call for little comment. In view of the purpose 
of the observations it was desirable to adjust the tilt of the object 
glass and plate with special care. It was also important that the 
setting on the field should be nearly exact. The sun appeared on 
the eclipse day in sufficient time to allow of the setting being made 
by means of the solar image; but arrangements had been tested 
by which the correct field would have been obtained if it had been 
cloudy up to totality.'^ The telescope was focused by trial photo- 
graphs of stars, and owing to the uniform temperature of the island 
the focus was unchanged for day observations. 
The object glass was stopped down to 8 inches for the eclipse photo- 
graphs and for all check and comparison photographs used in the 
reductions. 
29. The days preceding the eclipse were very cloudy. On the 
morning of May 29 there was a very heavy thunderstorm from about 
10 a. m. to 11.30 a. m. — a remarkable occurrence at that time of year. 
The sun then appeared for a few minutes, but the clouds gathered 
again. About half an hour before totality the crescent sun was 
glimpsed occasionally, and by 1.55 it could be seen continuously 
through drifting clouds. The calculated time of totality was from 
2 hours 13 minutes 5 seconds, to 2 hours 18 minutes 7 seconds, 
Greenwich mean time. Exposures were made according to the pre- 
pared program, and 16 plates were obtained. Mr. Cottingham gave 
the exposures and attended to the driving mechanism, and Professor 
Eddijigton changed the dark slides. It appears from the results 
that the cloud must have thinned considerably during the last third 
of totality, and some star images were shown on the later plates. 
The cloudier plates give very fine photographs of a remarkable 
prominence, which was on the limb of the sun. 
A few minutes after totality the sun was in a perfectly clear sky, 
but the clearance did not last long. It seems likely that the break-up 
■fThe method depended on setting the cross wires of the theodolite (attached to the 
coelostat) on a terrestrial mark, and then starting the clock at a particular instant. 
