42 S. P. Langley— Observations on Mount Etna. 
from them as far as I could, their opinions as to the conditions 
of observation at their respective positions. I found during a 
few days’ stay in Egypt, a sky which appeared to give almost 
unequalled definition. I carried no instruments with me, but 
by the kindness of General Stone, of the Khedive’s staff, had 
the loan of a small telescope, which used on several nights, 
from the roof of my hotel in Cairo. Judging by this (if the 
nights were fairly typical, as they seemed to be), the winter cli- 
mate of Kgypt must be almost unequalled for astronomical pur- 
poses, the transparency and definition being alike admirable, 
and the freedom from tremor such that the discs of the stars I 
examined, seemed fixed in the center of interference rings, as 
sharp and motionless as engraved lines. The days were uni- 
formly fine, but a slight haziness appeared, I thought, in the 
lower atmosphere, due, perhaps, to dust; which was surmounted 
y a moderate elevation. 
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