50 
FIRST REPORT—-1831. 
that by an extended comparison of observations, light may be 
thrown upon the anomalies which have been observed at Paris 
and in other places. 
V. That the Association should express its desire to receive 
a satisfactory exposition of the theory of the moistened bulb 
hygrometer , and that observers be also invited to institute series 
of comparative experiments on the indications of the moistened 
thermometer and the temperature of the dew point. 
Note . These indications may be ascertained by Mr. Dalton’s 
process, or by Mr. Darnell’s Hygrometer, or by both. 
Notwithstanding the ingenious and laborious researches 
of Hutton, De Saussure, Leslie, Anderson, and Gay- 
Lussac upon this subject, scientific deductions drawn 
from more extended experiments are greatly wanted. 
The simplicity and certainty of the experiment by which 
the cold produced by the evaporation of water is measur¬ 
ed, renders an accurate theory of the result peculiarly 
desirable. The experimenter would do w r ell to consult 
Mr. Dalton’s views on the theory of Hygrometry, con¬ 
tained in his Meteorological Essays , and in the Man¬ 
chester Transactions , and to examine the investigations 
of Professor Leslie, (. Relations of Heat and Moisture , 
and Supplement to the Encyclopedia Britannica, Article 
Meteorology ;) of Dr. Anderson ( Edinburgh Ency¬ 
clopedia , Article Hygrometer,) and of M. Gay-Lussac, 
(. Biot , Traitd de Physique , Tom . II.) A good series 
of observations at high temperatures will be found re¬ 
corded in Nos. II. and III. of a Calcutta Journal, enti¬ 
tled, Gleanings in Science. 
VI. That experiments on the Decrease of Temperature at 
increasing heights in the Atmosphere be recommended as an 
important subject for the contributions of observers. 
Note. Series of observations for considerable periods of time 
on the mean temperature of the air at fixed hours, and 
at stations of which the difference of height has been 
accurately measured, are the most valuable. The best 
hours for observation are those which give most accu¬ 
rately the mean temperature of the period of observa¬ 
tion. The hourly observations at Leith Fort have 
determined the hours which give the annual mean tem¬ 
perature in this country to be about 9J a.m. and 8J 
p.M. Experimental balloons have lately been employed 
to assist the solution of this problem, which is one of the 
most interesting in Meteorology ; but the investigation 
of it is nearly brought to a stand for want of sufficiently 
