54 Proceedings of the Royal Physical Society. 
months. The highest reading obtained by Hay at Manfalut 
below the First Cataract, in 1830, was 82°; the highest at 
Abu Simbel, in 1831, was 84°. Coutelle observed tempera- 
tures of 83°°7 at Phile. The lowest temperatures recorded by 
Hay, Schnepp, Russegger, and Chaix, during January, between 
Assouan and Minieh, varied from 54° to 58°°5; and between 
the First and Second Cataracts, Hay in this month obtained 
a minimum reading of 60°, and Villiers Stuart one of 58°. 
14. The river, no doubt, has an important influence on the 
temperature of the avr over it during some howrs of the day. 
In Part I., p. 207, I have shown that the Brahmaputra, when 
it possesses a temperature lower than the air both day and 
night, affects the air considerably at sunset, and but slightly 
in the heat of the day, lowering also the daily mean. The 
effect in summer would be to diminish the relative coolness 
of the Nile as regards the air, so that if I have erred at all it 
has been in understating the difference between the air and 
water temperatures. I do not think, however, that observa- 
tions of the air made on a house-boat, that retains at night 
the heat of the day, would much affect in summer the daily 
air mean, and my air data are mostly of this description. 
The whole matter is in need of an investigator. 
Suggestions for observing the temperature of the Nile. The 
method that involves least trouble merely consists in taking 
observations of the air and water at sunrise, an hour well 
suited to the habits of life on the Nile. For this purpose 
the same bath-thermometer can be advantageously employed. 
The air observation should be made first, and care should be 
taken to thoroughly empty the pocket after the water 
temperature has been observed. If more attention can be 
devoted to the inquiry, then maximum and minimum air 
readings should be taken, or, in the absence of self-recording 
instruments, observations of the air should be made with 
a common thermometer at sunrise, and in the afternoon at 
two o’clock in winter, and between three and four o’clock in 
summer, the corresponding river observations being taken at 
sunrise and sunset. In the case of the river, the thermometer 
of the bath pattern should be lowered to a depth of two or 
three feet, and must be kept there not less than three minutes. 
