The Total Solar Eclipse of 1900. 71 
water, it was soaked for a few minutes ina bath of tartrazine, and allowed to 
dry. It then was a fine yellow colour, and transmitted the green, yellow, 
and red part of the spectrum. As the photographic plate was made especially 
sensitive to the green, and not much to the yellow and red, it was not thought 
necessary to try to cut off that end of the spectrum by another screen of suitable 
colour. 
The image of the Sun was formed by an object-glass of 6 inches aperture and 
7 feet 103 inches focus, mounted at one end of a long wooden tube, which, at 
its other end, carried a plate-holder taking a plate 81 by 61. The light was 
fed into this camera by a fine ccelostat, made by Sir Howard Grubb, and kindly 
lent to me by the Royal Dublin Society and Royal Irish Academy. The plate 
was exposed for 80 secs., which was 5 secs. short of the calculated time of totality, 
but which turned out to be 3 secs. shorter. I developed the plate on my return 
home. I think it shows more detail up to the Sun’s limb than if the plate had 
been exposed without the screen, and also considerable extension in the outer 
corona (see fig. 3, Pl. vi.). It would have been of more interest if another 
photograph could have been taken simultaneously with another similar instrument 
without a screen. 
The spectroscopic observers report that the bright line in the green, due to 
coronium, was very faint in this eclipse, and in fact could not be seen by some. 
The planet Mercury appears on the plate. 
IQUE. 
Sir Howarp Grusp’s Report. 
The Instrumental equipment of the Expedition consisted of one ccelostat, 
worked in conjunction with a 6-in. object-glass of about 8 ft. focus, mounted on 
a camera, and used by Mr. W. E. Wilson for producing photographs through his 
yellow screen :— 
A second ccelostat, worked in conjunction with a specially corrected 4-in. 
object-glass of 19 ft. focus, mounted in a long wooden tube provided with a 
camera, and used by the Astronomer Royal for Ireland, and Prof. Bergin, for 
producing the large pictures :— 
An instrument of the kinematograph type, for producing a series of pictures 
of the spectrum of the chromosphere, etc., worked by Dr. Rambaut and Sir 
Howard Grubb. 
The only instruments that possess points of novelty and need be described are 
the ccelostat and the kinematograph instruments, 
