36 Proceedings of the Royal Physical Society. 
data at my disposal, a number of conclusions have been 
formed; and, for the more convenient treatment of the sub- 
ject, I will here state them in the form of propositions, which 
on the facts before me I will then endeavour to sustain. 
1. During its course below the Second Cataract the Nile 1s m 
summer markedly cooler than the air. This is capable of 
demonstration in several ways. The most obvious method 
lies in the comparison of the mean temperatures, such as 
will be found in Table I. below presented, which I have 
prepared from the observations of Robert Hay. Whether in 
the means of the individual months, or in the general mean, 
this striking feature of the Nile is there consistently 
illustrated, and we learn from its columns that in summer 
the Nile between the two lowest of the cataracts is on the 
average nearly twelve degrees cooler than the air, and about 
half way between the First Cataract and Cairo more than 
seven degrees cooler than the air. 
. 
TABLE I, 
The Nile in Summer (prepared from Hay’s observations). 
1830. 1831. 
Month. —_— — : — 
Locality. | Lat. N.} Air. | Water. W. diff. Locality. Lat. N. | Air, |Water.| W. diff. 
: [eae Sale SSS SS \- 
|May, .| Beni Hassan, 27°53’ 81:0) 74:0 | -—7°0 | Abu Simbel, 22° 20’| 88°5| 75 5 |-13 0 
June, as 27° 53’ | 84:0) 75°6 | —8°4] ,, PY 22° 20 | 90°0| 78-0 | -12°0 
palys | Tek. aes 27° 37’. 86°3| 784 | -7-9| ,, * 22° 20'| 92-1 | 78°8 |—13°3 
| August, | Manfalut, 27° 23" 85 dl (97) =O - | 22° 20’| 91°2| 82°6 | —8°6 
7 ae ia 5 | 
| ye z B 
Mean 84 ou 76°9 | —7:4 Mean | 90°4} 78°7 |—11°7 
Although the indications in this table are sufficiently 
clear, it might with justice be asked whether the data 
afforded by other observers similarly demonstrate the 
great coolness of the river in summer in comparison with 
the air. It will be enough for the present to refer to the 
observations of the river temperature. Captain Newbold 
found the mean temperature of the Nile for July (1840 2) 
between Cairo and Thebes to be 79°5. This is near the 
mean for July, namely 78°4, obtained from Hay’s observa- 
tions in the vicinity of Tel, about half way between these 
—_—" 
