250 



NA TURE 



[January ii, 1900 



•sponded (by previous adjustment) to the centre of the 

 jplate in the prismatic camera. He had a timekeeper to 

 rrecord the times of contact. 



Fig. 4. — Six-inch prismatic camera 



A third acted as timekeeper to record the exact 

 moments at which the exposures were begun and ended. 



A fourth volunteer, by means of a piece of cardboard, 

 covered and uncovered 

 the front of the prism, 

 ^from directions given 

 by Mr. Fowler and Dr. 

 Lockyer respectively. 



In one case two, and 

 ,in another three, men 

 were required to hand 

 and receive the large 

 dark slides before and 

 after exposure, taking 

 them out of, or placing 

 them back in, bags 

 .made for this purpose. 



Six-inch Prismatic 

 Camera. 



This instrument, the 

 •dispersion of which had 

 been increased by the 

 addition of a second 

 prism, was worked by 

 Mr. Fowler, with the 

 assistance of Lieut, de 

 Wet and five men. Mr. 

 J owler's programme 

 ■was to begin taking a 

 series of ten snap-shot 

 ipictures five seconds 

 before the commence- 

 ment of totality, to ob- Fi 

 tain a record every 



second or thereabouts of the spectrum of the chromo- 

 sphere. After this he exposed eight other plates to 

 secure photographs of the coronal rings, the exposures 



being of various lengths. It was also arranged that 

 at five seconds before the end of totality he should com- 

 mence another series of ten snap-shots, exposing the 

 • last of these some few 

 seconds after totality. 



Nine-inch Prismatic 

 Camera. 



This instrument was 

 in charge of Dr. W. J. 

 S. Lockyer, who was 

 assisted by Lieut. Per- 

 cival Jones, R.N.R., and 

 six men. This instru- 

 ment was also fed by a 

 siderostat, but the tube 

 was not placed horizon- 

 tally. It was intended 

 with one of the prismatic 

 cameras to so mount 

 the tube that the arcs 

 formed on the photo- 

 graphic plate should be 

 symmetrical about the 

 direction of dispersion, 

 and it was decided that 

 the 9 - inch camera 

 should adopt this plan 

 of mounting. 



The exact position of 

 the tube to obtain this 

 result was carefully de- 

 termined by calculation. 

 To facilitate the erec- 

 tion of the instrument at 

 the station two wooden 



frames to carry the tube were previously made and taken 



out. 



It is satisfactory to state that the photographs showed 



KO. 1576, VOL. 61] 



5. — Nine-inch prismatic camera. 



that the experiment was very successful, the arcs coming 

 out exactly as forecasted. 



Although this instrument was capable of only giving 



