Report on tlte Solar Eclipse Expedition to Viziadrug. 33 



in the centre of the field of view which corresponded (by previous 

 adjustment) to the centre of the plate in the prismatic camera, 

 fle had a timekeeper to record the times of contact. 



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 or placing them back in bags made for this purpose. 



Six-inch Prismatic Camera. 



This instrument, the dispersion of which had been increased 

 this year by the addition of a second prism, was worked by 

 Mr. Fowler, with the assistance of Lieut, de Wet and five men. 

 Mr. Fowler's programme was to begin taking a series of ten snap-shot 

 pictures five seconds before the commencement of totality, to obtain 

 a record every second or thereabouts of the spectrum of the chromo- 

 sphere. After this he exposed eight other plates to secure photo- 

 graphs 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 commence another series of ten snap-shots, exposing the 

 last of these some few seconds after totality. On developing the 

 plates it was found that everything had gone satisfactorily. The 

 large plates containing the ten snap-shots give the whole story of 

 the chromosphere during twelve seconds, the time to make the ten 

 exposures, and in one of the negatives there are as many as a 

 thousand lines (about). 



The last set of ten exposures did not come out quite as expected, 

 for the reason that the duration of totality was a few seconds shorter 

 than had been provided for in the time table, so that only two of the 

 exposures were made before the end of totality. The very last 

 exposure, however, taking about nine seconds after totality, shows 

 many bright lines. 



Nine-inch Prismatic Camera. 



This instrument was in charge of Dr. W. J. S. Lockyer, who was 

 assisted by Lieut. Percival Jones, R.N.R., and six men. This in- 

 strument was also fed by a siderostat, but the tube was not placed 

 torizontally. It was intended with one of the prismatic cameras to 

 mount the tube that the arcs formed on the photographic plate 

 should be symmetrical about the direction of dispersion, and it was 

 lecided that the 9-inch camera should adopt this plan of mounting. 



VOL. LXIV. D 



