254 
CAPTAIN W. DE W. ABNEY AND DR. A. SCHUSTER 
order of the Khedive, and was in charge of the joint expeditions during their stay at 
Sohag. Great thanks are due to his unremitting zeal and energy; his aid in 
erecting the observatory and telescopes proved of great value, and his mechanical skill 
helped the expedition over great difficulties. 
Esmatt Effendi, also a member of the Khedive’s household, gave most valuable 
assistance, and to him, as well as to many others equally able and anxious to help, our 
thanks are due. 
II .—Preparat ions for totality. 
The observatory was built on a level piece of ground close to the banks of the Nile. 
It was surrounded by a double wall of sugar-canes, affording an efficient protection 
against the dust which occasionally was carried in large quantities along the river. 
The ground in the immediate vicinity of the observatory was, in addition, constantly 
kept wet by watermen, so that the danger to the instruments from the dust and 
sand was reduced to a minimum. 
Half of the ground covered by the English station was taken up by Mr. Loceyer’s 
large equatoreal telescope, while the other half was reserved for the photographic 
instruments. The present report only refers to the results obtained with the latter. 
A double layer of bricks afforded a sufficiently firm foundation for the stand on which 
the cameras were mounted. The stand and clockwork had originally been made for 
the transit of Venus expedition of 1874, and on that occasion supported one of the 
photoheliographs, but during this eclipse it had to carry three cameras. An achro¬ 
matic lens of 4 inches clear aperture, having a focal length of 5 feet 3^ inches, 
was reserved for the photographs of the corona itself. The image of the moon taken 
with this lens during the eclipse had a radius of - 29 of an inch. The second camera, 
carried on the same stand, was on a similar principle to that first used during the 
Siamese eclipse of 1875, and then called a prismatic camera. It was an ordinary 
camera with a prism placed in front of the lens. The prism used on this occasion was 
of white and dense flint glass, and instead of an angle of 8° it had a refracting angle of 
60°, and each face had a surface of 3 inches square. The corrected lens used with 
the prism had a focal length of 20 inches for the yellow rays. As the plates exposed 
in this camera were sensitive in the red as well as in the blue, it was impossible to 
obtain the whole range of the photographic spectrum in focus on the plate, but in 
order to obtain the best results the back of the camera which carried the sensitive 
plate could be tilted so as to bring a larger range of the spectrum into focus at the 
same time. Nevertheless, an inspection of the plates obtained in this camera shows 
that the parts extending from the green into the infra-red are the only ones which are 
properly in focus, and it is to these parts that our attention was chiefly directed with 
this instrument. 
To the third camera was attached a complete spectroscope. A lens of 2 inches 
aperture and 11 inches focal length served to form an image of the corona on the slit. 
