River Temperature. 291 
river. From the means of the observations, Dr Borius infers 
that the surface was 0°4 (C.), or 0°°7 (F.), cooler than the 
water 5 metres deep. On carefully going over his figures, I 
make the surface on the average only 0°-05 (C.), or 0°09 (F.), 
cooler than the greater depth. The difference, however, is 
in either case small, and it is scarcely worth while at present 
to discuss its nature or its origin. From an analysis I have 
made of these results, I gather that at 6 a.m. the surface was 
cooler by one- or two-tenths of a degree Centigrade, whilst at 
10 A.M. it was warmer to the same extent. The comparisons 
varied much at noon and at 4 P.M., the difference being 
sometimes an excess of one- or two-tenths for the surface, 
or of two- or three-tenths for the greater depth, whilst 
occasionally the temperatures were the same. At 8 P.M, 
either the surface was a couple of tenths cooler or there was 
no difference at all. We thus see that the surface-heating, 
when it was apparent, was very slight, and was noticeable 
only in the heat of the day. The slight coolness of the 
surface, also not uncommon in the daytime, Dr Borius 
attributes. to the heavy rains which the party at times 
experienced. On one occasion when the river was 27°°6 
(C.), and the air 28°-4, the temperature of the rain proved to 
be 22°4. 
In the spring of 1885 Dr Marcet made some observations 
on the temperature of the Lower Nile, and, though unable 
to obtain any definite results from his experiments, he 
arrived at the conclusion that, owing to the thorough mixing 
of the water arising from the winding course of the river, 
and from the unevenness of its bed, the temperature must 
have been nearly the same throughout its depth, which was 
sometimes 5 fathoms and over. 
Before proceeding to refer to my own observations on the 
Thames and its tributaries, I should remark that precise data 
for great rivers are apparently scanty. We want to know 
something more of the Congo at Vivi and its reputed depth 
of 90 fathoms, of the Yangtse with its depth, for instance at 
Hankow, of 70 or 80 feet, whilst even of the Mississippi my 
information as yet is only of a general character. We require 
much to supplement Mr Révy’s solitary observation on the 
