CHEMICAL AND PHYSICAL NOTES. 133 
observations were made by moving the thermometer at different 
velocities in the air of the room, and observing the rates of cooling. 
Dealing only with low velocities it was found that while in perfectly 
still air the term was 65 seconds; when moving through the air at 
the rate of 2 m. per second the term was 17:2 seconds; and when 
the velocity was 1 m. per second it was 24°6 m. per second; while at 
0:5 m. per second the term was 30 seconds. Allowing that, whether 
moved or not, the cooling of the thermometer goes on independently 
at the still-air rate of @; per second, and subtracting this from the 
reciprocals of the above numbers, we have the rates of cooling due to 
motion of the air ;—at the rate of 2m. sb, of 1 m. 75, and of 4 m. per 
second 2, the rate of cooling in calm air being g. The reciprocals 
of these fractions, or the terms, are 24, 40, 56 and 65, which are in 
the proportion 3:5:7:8. 
Taste XIV. 
Time P.M. 
Excess. 12,45 1°10 1.40 2.10 6.30 
Duration of Half-fall in Seconds. 
12° C. 26 és 33 22 36 
10° C. 25 2 36 22 36 
8° C. 27 31 36 25 35 
6° C. 27 31 30 31 33 
Mean 26°25 31 33°75 25 35 
Term 37°9 44°7 48°7 36°0 50°5 
The importance of these figures is that they show that thermo- 
meters in the open air, even when the air appears to be calm, are in 
reality well ventilated. In a room, the temperature of the dry bulb, 
and still more that of the wet bulb, are very imperfectly given by a 
stationary thermometer; both thermometers must be whirled in 
order to get anything like exact observations. In the thermometer 
screens of a meteorological station the instruments are certainly well 
ventilated when there is a wind; and we see that, even in a calm, 
the ventilation may be sufficient. 
The Thermometer as a Calorimeter.—The term of cooling of a 
thermometer and the method of its determination have been dwelt 
on at considerable length, because the information regarding it to be 
found in manuals is usually defective. The same remark applies to 
