302 Proceedings of the Royal Physical Socvety. 
Tidal influence will probably not affect the regular rise. 
and fall of river temperature very much, as long as it merely 
results in the to-and-fro movement of the same body of fresh 
water. There is no evidence of any such interference in the 
tables which Sir George Airy gives for the Thames at Green- 
wich, though I can only found this opinion on the similarity 
in amount of the river’s daily range above and within tidal 
influence, as at Kingston and Greenwich. The unusually 
limited daily range of the Weser at Elsfleth seems to indicate 
some direct access of sea-water, though the absence of such 
an influence is expressly stated. The Senegal at its mouth, 
off the Island of St Louis, exhibits in August and September 
very irregular daily fluctuations, and as often as not no rise 
at all. In this season, according to Captain Borius, the 
water was potable, but it is apparent that the salt-water 
had some access, though the mixture was not so noticeable 
as in other times of the year. 
With regard to the diurnal ranges of rivers generally, it is 
a remarkable fact that great differences in the size of rivers 
are not represented by great contrasts in the amount of the 
daily range. I do not here include very small rivers, but 
those that are not smaller than the Thames, or the Seine, or 
the Loir, and which may be as large as the Nile. Renou 
gives for the Loir in March a mean daily range of 1°-0 (F.), 
and this is just what I have estimated for the Thames in the 
same month. Dr Marcet’s observations give a mean for the 
Lower Nile in March of 1°°6. In both the Thames and the 
Seine, according to my own observations and those of Renou, 
the diurnal range is rarely if ever as much as 3°:0, whilst the 
mean for the year in the case of both rivers is somewhere 
about 1°°5. These figures strike one as having little relation 
to the great disparity in size between these two rivers on the 
one side, and the Senegal and the Rio Negro on the other, 
both of which, according to the observations of Borius and 
Wallace, would have in the hottest month a_daily range of 
about 1°°3. Then, again, the daily range of the Thames at 
_ Kingston is no greater than that of the Brahmaputra at 
Sadiya, neither being over 2°. 
When, however, we look into the matter, we find that we 
