River Temperature. 55 
Special points should be also investigated, such as the 
change of water temperature when the river begins to rise. 
Captain Newbold records that the temperature of the Nile 
between Cairo and Thebes was increased from 79° to 80° 
“at the commencement of the inundation in June by the 
freshes from Abyssinia.” The relation of the temperature of 
the river to the velocity of the current should be attended 
to; and it might be expected that the difference in the river 
temperature between two localities, such as Cairo and 
Assouan, would be less when the river runs swiftly than 
when it is sluggish. The difference between the air tempera- 
ture on the river and on the land, some distance from the 
banks, requires to be worked out for the various seasons ; 
and two or three days each month might be devoted to this 
object, the observations being taken at sunrise, in the after- 
noon, at sunset, and at midnight. The influence of the 
northerly winds, or Etesian breezes, in lowering the river 
temperature should be recorded. Dr Marcet noticed a 
considerable effect thus produced in March. It would be 
also worth while inquiring into the variation of the Nile’s 
temperature with depth. For this purpose Messrs Negretti 
and Zambra, of London (Holborn Circus), supply a useful 
instrument on the Sixe pattern for about a guinea, and 
a reference thermometer (certified at Kew) for checking its 
readings for about fifteen shillings. 
TABLE XIIa. 
A few Observations on the Temperature of the Nile at Cairo 
and in tts Vicinity. 
January 2s 1837, . | Between Cairo and Benisouef, | Russegger, _. | Nile mean temp. 60°7. 
AR Teas |PAtsBenisOucia « << ~ « «| Chaix’< 2 <1 33 3 », 09°9. 
at ay, . | At Benisouef, . . Chaix, . . a J >» 5Or4: 
February 17-20, 1879, Between Cairo and Benisouef, Villiers Stuart, ‘; fen 100°0: 
April 12-18, 1836, . | At Terraneh, .. . | Russegger, .| ,, 3 ay 8 1 Or2e 
Satin ¢ Pe EAS CALL Oram a tania <i Foun <tc ae 3 a »  79°0. 
December 6-8, 1878, | Between Cairo and Benisouef, | Villiers Stuart, | _,, 7} 5) -66°0: 
5 134 14, 1836, At Cairo,. . Russegrers "S|" 5, 5 ae" ‘606: 
oF 28-29) 1846, Between Wardan and Terraneh, Chaix es i = || ss i a G04: 
35) 3051859: “> | At Benisonef, . . . . =. .|Schnepp, ...|. ;, . 33 . 60°0: 
1 Computed from the observations of Newbold between Cairo and Thebes, and of Hay 
at Beni Hassan. 
