1896-97.] Notes on the Total Eclipse of the Sun. 491 
The tube was made of thin galvanised iron in 8-foot lengths, suit- 
ably tapered to facilitate packing and fitting together, the lower 
end being 26 inches in diameter, the upper 12 inches. The lens 
was mounted on a metal carrier securely fixed on the top of a 
substantial wooden tripod, and was adjusted by means of a delicate 
centring apparatus. In order to prevent possible vibration of the 
tube from disturbing the lens, it was connected with the tube by a 
collar of black cloth only. The exposing shutter at the upper end 
of the tube was opened by a cord passing into the hut in which the 
observer was stationed ; on slackening the cord, the shutter closed 
of itself. At the lower end of the tube a small dark room was 
built of strong brown paper covered with waterproof material. In 
this dark room was mounted the slide for the photographic plates, 
which is here shown. The angle between the plane of the plate 
and the vertical is, of course, the altitude of the sun at totality, 
while the inclination of the slide to the horizon in that plane is the 
parallactic angle plus a small correction for the sun’s motion in 
declination and the change of refraction, The driving-clock, which 
was kindly lent by Lord McLaren, is so arranged as to move the 
plate at a uniform speed of L913 inch per minute, corresponding 
to the apparent angular motion of the sun. The operator stationed 
in the dark room had sufficient space at his disposal to allow of his 
putting the plates in position during the eclipse, and was at the 
same time able to see the sun’s image on the sensitive film. The 
o 
plates used were 18 inches square, so as to give a picture of a large 
part of the corona. By arranging four lead pencils carried by 
levers, we were able to use the slide motion as a chronograph for 
recording the approximate exposures made by all the observers. 
2. The 6-inch Simms telescope , with its large prism in front of 
the object-glass, was mounted on a heavy Cooke equatorial stand 
with driving-clock. The advantage of this form of instrument is 
that, in the case of a stellar spectrum, the source of light being a 
point at infinite distance, no slit or collimator is required ; while in 
the case of the eclipsed sun the ring of chromosphere acts like a 
narrow slit of circular shape, and we obtain a series of overlapping- 
rings corresponding to the various ref rangibili ties of the light given 
out by the chromosphere. Provision was made for nine exposures 
with this telescope. 
