88 Prof. Marcet on the Variations of the Temperature 
without difficulty, in elevating it, I had it fixed vertically in 
the ground to the depth of six or seven feet. Various pre- 
cautions had been taken to prevent it being broken or over- 
thrown by the violence of the wind. It was placed in circum- 
stances most favourable for experiments of this nature, that 
is, situated in the middle of a large meadow, at a pretty con- 
siderable distance from any kind of dwelling, and even from 
groups of trees of any size. Along the mast, at intervals of 
ten feet, I had placed horizontal bars of fir two feet in length, 
each having a small pulley at the extremity for the purpose 
of raising and bringing down the thermometers. The ther- 
mometers themselves, which were extremely sensitive and of 
large size, had their balls covered with a pretty thick layer of 
a non-conducting substance, such as soft wax, or unspun cotton, 
in order that their temperature might not vary during the 
time necessary to bring them down from their elevated posi- 
tion.* At the moment of every thermometrical observation, 
I noted the state of the atmosphere in its different meteoro- 
logical relations, and on most occasions I examined Leslie’s 
ethrioscope, as well as Saussure’s hygrometer. 
The principal object I had in view by undertaking these 
researches, may be reduced to the solution of the four follow- 
ing questions :— 
1s¢, How far is the increase of temperature which takes 
place at certain times of the day in proportion as we ascend, 
influenced by the state of the sky and the agitation of the air ? 
2dly, To determine the times of the day at which this in- 
crease of temperature commences ; does it continue constant, 
or shew a tendency to augment during the night ? 
3dly, Is the limit of elevation at which the increase of tem- 
perature ceases constant, or does it vary according to the me- 
teorological state of the atmosphere ? 
4thly, Do the increase of temperature, as well as its limit in 
regard to elevation, remain constant, or do they vary accord- 
ing to the different seasons of the year? 
* This interval never exceeded three quarters of a minute. The balls of 
the thermometers were so protected, that a difference of temperature amount- 
ing to five degrees did not begin to affect them for about a minute. 
