308 Proceedings of the Royal Physical Society. 
putra table :—To correct for the water’s chill the day’s mean 
of air observations made on a large river, add to it two-thirds 
of its excess over the day’s mean of the water temperature. 
Thus, with a mean water temperature of 60° (F.), and a mean 
for the air on a river of 69°, the corrected air mean would be 
75°. From this table we can also calculate the corrections 
for particular hours. Thus, for 2 P.M., only one-fifteenth of 
the excess, and for 6 P.M. as much as one and a half times 
the excess, must be added; whilst for 6 A.M. the plus correc- 
tion would be five-eighths. I have here spoken only of 
large rivers. Air observations on small rivers would prob- 
ably be but little affected, as long as the air is in motion. 
Of this the Kundeel affords an example. 
In concluding the first part of this paper, I must lay stress 
on the value of all observations on river temperature. No 
period ought to be too short for making useful additions to 
our knowledge of the subject, and I trust that observers in 
different parts of the globe will take advantage of oppor- 
tunities that lie at their doors. Three thermometers, 
properly tested, would be required. For the air a maximum 
and a minimum thermometer, and for the water an ordinary 
thermometer of the bath pattern. I have tried some half a 
dozen different plans of taking the water temperature, but 
have found none so good as sinking a bath thermometer 2 
or 3 feet below the surface and leaving it there two or three 
minutes. It is essential that the immersion of the bulb 
should be sufficient, since many thermometers will not stand 
the test of being drawn up 10 feet in the cold air after 
standing in water twelve or fifteen degrees warmer than the 
air, a not uncommon condition of things at sunrise. The 
instruments made by Negretti & Zambra, on the pattern of 
those used in the British Navy for sea-temperature, will 
stand this test. Of course, a good substitute for a bath 
thermometer can be obtained by fixing an ordinary ther- 
mometer in a bottle and reading through the glass. For 
rapidity, I have often employed a sensitive chemical ther- 
- mometer that reads in ten or fifteen seconds, placing it in a 
large bottle of the river water and reading it there. This is 
an excellent plan when making a series of comparative 
