490 Proceedings of Royal Society of Edinburgh. [sess. 
2. Visual telescopic observations of the corona and prominences. 
3. Visual spectroscopic observations of the chromosphere, and 
polariscope observations of the corona. 
4. Direct photographic records of the corona and prominences. 
5. Photographic records of the chromosphere and other solar 
envelopes. 
As the photographic methods are at present the most likely to 
add to our knowledge of the sun’s constitution, we decided to 
direct all our efforts to the fitting out of a photographic equipment 
which should include apparatus of as efficient and varied a charac- 
ter as possible. This could be effected with little difficulty, as the 
Edinburgh Royal Observatory possesses a variety of spectroscopes 
and cameras well suited for an eclipse expedition. The instruments 
we took with us comprised : — 
1. A forty-foot telescope with Dallmeyer photographic lens of 
4 inches aperture. 
2. A 6-inch equatorial with object-glass prism. 
3. A camera with a quartz lens of 1*8 inch aperture and Iceland- 
spar prism, mounted on the same stand as the 6-inch 
equatorial. 
4. A camera of 4 inches aperture and 33 inches focal length, 
equatorially mounted. 
5. A whole-plate camera by Dallmeyer with a lens of 1^ inch 
aperture and 10 inch focus. 
These instruments we shall describe a little more fully, 
1. 40 -foot telescope . — The object in employing a telescope of great 
focal length is to obtain large direct negatives of the sun, which 
require no further enlargement. The diameter of the sun’s image 
in this instrument is dy 1 ^- inches But since it is impracticable, on 
an expedition at least, to mount a tube of this length equatorially, 
the difficulty of following the sun’s diurnal motion was overcome 
by fixing the tube on wooden trestles so as to point exactly to the 
place in the heavens which the sun would occupy at mid-eclipse, 
the photographic plate being mounted on a slide which moved in 
the proper direction and at the speed required to keep the sun’s 
image central. This plan had already been employed with great 
success by Prof. Schaeberle, of the Lick Observatory, in Chili, in 
1893, but our instrument was the first of the kind tried in Europe. 
