ON ANEMOMETRY. 349 
_ The truth of the theory may therefore be regarded as established, the 
small differences being quite unimportant. 
On regarding attentively the columns A, B, it will be seen that the pro- 
gression of each is nearly similar, from which it follows that C, their differ- 
ence—representing their cooling power of evaporation—contains a series of 
numbers nearly proportioned to B. Ranging these columns side by side, and 
reducing to the same mean values, we have 
B. Cc. E. 
83 84. | 82 
62 69 61 
43 53 45 
From which it follows, that for temperatures of the wet bulb above 
_ that of the atmosphere, we may disregard the correction in column A, and 
take the whole cooling effect of air and vapour, as proportioned to the va- 
porizing force. The problem is thus simplified for practical use. 
To judge if the same rule applies when the temperature of the wet bulb is 
below that of the atmosphere, the following sets of experiments were made 
in the open air, with variable differences between the temperature of the air 
and that of the wet bulb (air 75°, evap. 63°):— 
Temperature of I. Il. Ill. IV. 
air above that | Thermometer | Thermometer | Thermometer {Mean of observed) 
of wet bulb. at rest. swung slowly. | swung faster. times. 
10” 17” 13” 12” 14:0” 
9 18 13 11 14:0 
8 19 14 15 16:0 
7 20 20 16 18°6 
6 26 24 17 22:3 
b) 30 26 24 26°6 
The numbers in columns I. II. IIL. TV. represent the seconds of time in cooling 1° of the wet 
__ thermometer. 
With the mean of the times we may compare a series of numbers propor- 
‘tioned to the vaporizing force due to the temperatures, in the given condi- 
tion of air, as under :— . 
Tempera f Mean of 
air asore tit observed Cepigied 
of wet bulb. times. 
10 14:0 13°0 
9). 14:0 14°4 
8 16:0 16°3 
7 18°6 18°6 
6 22:3 21°6 
5 
26°6 ° 26°1 
_ From which it appears that the rate of cooling of the wet bulb is still 
nearly proportional to the force of vaporization, until the temperature of the 
wet bulb deviates much from that of the atmosphere. 
