NOTES ON PLATE EXPOSURES. 185 
NOTES on PLATE HXPOSURHS, AND THE SUBSEQUENT 
PHOTOGRAPHIC TRHATMENT ADOPTED BY THE 
SYDNEY UNIVERSITY ECLIPSH EXPEDITION. 
By EpeGar H. BOOTH, B.S<., 
Lecturer in Physics in the University of Sydney. 
[With Plates VII—VIII.] 
[Read before the Royal Society of N. 8. Wales, November 1, 1922. } 
A very important portion of the work of any WHclipse 
Expedition is photographic. Indeed, photographic methods. 
are of great value in any branch of scientific work in which 
they can be employed, on account of the possibility of 
obtaining a permanent record for later analysis. 
The cameras at our disposal for photographs of the 
corona were varied both in their magnifications and in their 
adaptability for the work in hand, but were so altered and: 
adjusted as to cover a wide range of inner and outer corona 
work. 
This paper is concerned purely with, the exposures and 
photographic treatment, but a brief description of the 
apparatus employed by the various members of the expe- 
dition is essential. It comprised:— 
(1) The Sydney University Cecil Darley Telescope, rigidly 
mounted horizontally as a coronagraph of equivalent focal 
length of sixteen feet, fed by a coelostat, and intended for 
work on the inner corona and prominences. Owing to 
slight distortion, only a diameter equivalent to 1°8 solar 
diameters could be relied on to give a dependable image, 
so a diaphragm was inserted to cut it down to that plate 
area. Half-plate slides were employed, the plates being 
Imperial Special Sensitive, backed. 
