240 Mr. F. W. Dyson. 



Engineer Townsend Set heliostat for corona spectrum, and again 

 for second contact. 



Surgeon Nimmo Exposed at object glass of Thompson coronagraph. 

 Observed duration. 



Seven men from the " Pigmy " also assisted ; two counting seconds 

 with the aid of a metronome ; one exposing in front of the condensing 

 lenses for the spectroscope ; one exposing in front of the object glasses 

 of the double camera ; and three assisting in handing plate holders to 

 Mr. Dyson and Captain Oldham. 



The mode of procedure, which was carefully rehearsed on several 

 occasions previously, was as follows : The observers were stationed 

 at their instruments, and Lieut. Frewen watched the diminishing 

 length of the crescent of the sun on the ground glass of the corona- 

 graph. He had a paper scale on which the lengths of the crescent were 

 marked, computed at intervals of 3 m , 2 m , l m , 30 s , 20", 10 s before totality. 

 At 3 m before totality Mr. Frewen called out " Stand by," and the 

 metronome, which had been carefully rated, was started. At l m before 

 totality he called out " Get ready." At the words " Thirty seconds " 

 Mr. Dyson and Mr. Atkinson drew out the dark slides ready for 

 exposure. At the word " Ten " the exposures for the " flash " spectrum 

 were begun. At the word " Now " given at the moment of totality 

 the time was recorded by Lieut. Oldham and Dr. Nimmo. Six 

 seconds after totality Mr. Dyson and Mr. Atkinson changed the plates 

 of the spectra and exposed for the corona spectrum, Mr. Townsend 

 moving the image on the slit by the heliostat. Mr. Dyson then went 

 to the Thompson coronagraph and made exposures as detailed below, 

 while Lieut. Oldham exposed with the double camera. When the 

 exposures with the Thompson were finished, about 30 s before the end 

 of totality, Mr. Dyson returned to the spectroscope, where he and 

 Mr. Atkinson changed the plates ready for the second flash, and 

 Lieut. Frewen returned to the ground glass of the coronagraph, 

 calling out " Now " at the instant of re-appearance, the times being 

 noted as before by Lieut, and Com. Oldham, and by Surgeon Nimmo. 



The Day of the Eclipse. From May 1 to May 1 3 the weather was 

 very fine in the early mornings, but the sky became overcast later in 

 the day. On some of these days the observing conditions at the time 

 of the eclipse were excellent, and on all were moderately good. On 

 May 13, however, there was a heavy thunderstorm, and till May 17 the 

 sky was generally overcast about noon. May 17 was a very wet day, 

 and on May 18, the day of the eclipse, it was completely overcast at 

 6 h . At 8 h it began to clear, but during totality there was a good deal 

 of light cloud in front of the sun. At 1 o'clock the sky was perfectly 

 clear. 



The following readings of the dry-bulb thermometer were taken on 

 the day of the eclipse : 



