River Temperature. 49 
TABLE IX.1 
Temperature of the Congo at Vivi (prepared from the 
observations of Dr A. Von Danckelman). 
| | 
Date. Air. |Water W.Excess. | Date, Air. Water W.Excess. | 
June 1882, | 73°2|81-1| 7-9 | January 1883, |78-4|82°8| 4:4 
July 5 69°3 | 78°8 9°5 February ,, 69°0:| 82°2)| BtZ 
August 43 70°5 | 76°3 5°8 March Me 79°2 | 83°7 4°5 
Saptember ,, | 75:2|77:7| 2:5 | April »» | 7861840] 5-4 
October ,, |77:°4/82°0| 4:6 | May 5, |78°3|83°7| 5:4 
November ,, 78°6 | 83°4 4°8 August as TOURS) oe 
December ,, 77°9 | 81°7 3°8 
From the Congo I pass to the Mississippi, which will be 
regarded here mainly from the contrast it presents to the 
Nile. A glance at the chart of the curves will be sufficient 
to show how remarkably the type of its thermal regime 
diverges from that of a river like the Congo, and, I may here 
add, from that of the Amazon. On account of the chilling 
influence of the waters from the colder and more elevated 
regions of the north, the temperature of the Mississippi at 
New Orleans is lower than that of the air during eight 
months of the twelve; and it is only in the latter part of the 
summer and in the first part of the autumn (August: to 
November in 1851, and July to October in 1852) that the 
river gains the ascendancy. At Memphis, five degrees 
farther north, the river temperature exceeds that of the air 
between June and November; and it is only during about 
five months, from January to May, that the cool waters from 
more northern latitudes give to the Mississippi a temperature 
lower than that of the air. 
In the curves of the Nile we find no analogy to those of 
1 Tn his ascent from the mouth of the Congo to a little above the Yellala 
Falls, during July and August 1816, Captain Tuckey found that the tempera- 
ture of the river varied between 75° and 78°. The mean temperature of the 
river at noon in the neighbourhood of Boma during July 20-31 was 
76°'1, and 76°°7 in the vicinity of Vivi and the Yellala Falls during August 
-20. 
‘, the middle of September 1863 the temperature of the river about Vivi 
aud the Yellala Falls varied, according to Captain Burton, between 75° 
and 79°. 
VOL. XIII. D 
