River Temperature. 35 
by him to volume exxxv. of the Philosophical Transactions, 
and volume xl. of the Ldinburgh New Philosophical Jowrnal. 
Notwithstanding this, the means there given form a valuable 
check to Hay’s summer observations at Beni Hassan. 
Professor Chaix in December 1846, and in January and 
February 1847, devoted some of his attention to the river’s 
temperature between Terraneh and Phile; and his results 
were subsequently included in a paper in volume xix. of the 
Journal of the Royal Geographical Society. Dr Schnepp in 
January 1860, during his voyage to and fro between Cairo 
and Philze, made some valuable observations, which are to be 
found in his book “Du Climat de Egypte.” Between 
December 1878 and February 1879, Mr H. Villiers Stuart, in 
a voyage from Cairo to Abu Simbel and back, made a valuable 
set of sunrise observations on the temperature of this river, 
which are given in his “ Nile Gleanings.” His unbroken series 
of temperatures, both of the air (maximum and minimum) and 
of the water, made during his ascent from Cairo to Abu Simbel, 
is unique of its kind; and his January observations above the 
First Cataract are my check on the winter observations of 
Hay in that region. Then follow some interesting investiga- 
tions of Dr Marcet in March 1885 between Siout and Edfou, 
the results of which will be found in volume xi. of the Quarterly 
Journal of the Royal Meteorological Society. 
With these materials at my disposal, I have been able to 
construct the thermal regime of the Nile in a manner 
sufficiently accurate for the purpose of a preliminary 
investigation. Profiting by a suggestion of Dr Ule in one of 
his papers on the temperature of the Saale, I have to a great 
extent avoided the disturbing influence arising from seasonal 
variation in different years, by making but slight use of the 
actual water temperatures in comparing different periods, 
and by mainly relying on an element largely independent of 
such variations, namely, the difference between the air and 
water temperatures. After a careful consideration of the 
1 The air observations were in most cases made on the river. The means 
deduced from them correspond closely, as will be subsequently shown, with 
recent Meteorological evidence; but for reasons given at the close of this 
paper, I don’t think that the daily means are much affected by the river. 
