On Ascertaining Mean Temperature. 85 
‘Art. VII.—On the Construction of an Instrument for Ascer- 
taining the Mean Temperature of any Place. By Dr. E. 
DAVEY. 
To ascertain the mean temperature of the year, and especially 
of particular months of the year, in different regions of the 
world, is an object of prime importance in Meteorology. The 
mean temperature of particular days is also of interest, though 
much less important. 
The mean temperature of the year may be pretty nearly 
inferred from observations on the heat of the earth, at a 
certain distance, say ten feet, from the surface, where it is 
almost beyond the reach of influence from the seasons; and 
the results thus obtained will probably be almost exact if 
taken at opposite seasons of the year. By this method, how- 
ever, we are informed rather of the average temperature of 
a succession of years, than of any. particular year, and we are 
by no means enlightened as to the differences of the seasons. 
The mean temperature of particular days may be, of course, 
ascertained by hourly observations on the thermometer, and 
taking their mean ; and the temperature of the month would 
be calculated from the mean of the days. This method is, 
however, obviously. too troublesome to be carried into 
practice. 
It was remarked by Humboldt, from observations made in 
France, that the temperature at sun-down, is in general 
pretty nearly the mean of the highest and lowest of the 
twenty-four hours: the lowest being at sun-rise, and the 
highest, about two hoursafter noon. He preferred, however, to 
take the actual mean of the two extremes. ‘These extreme 
points may be very exactly ascertained by means of the instru- 
ment well known as Six’s day and night or register thermome- 
ter, which leaves a mark of the highest and lowest points which 
the thermometer has attained since the last previous observa- 
tion. 
The description of my sensitive thermometer pendulum has 
reference to the drawing. It consists of a glass tube, fixed 
upon any suitable frame, A being the axis of oscillation. 
The glass tube is bent in the form of a reversed syphon, of 
which each limb, but necessarily the limb G E F, is upwards 
of thirty-two inches in length. It contains three bulbs, of 
which the bulb B and part of C D down to D. with the 
intervening tube contains air.—The remaining portion of the 
bulb C D and part of the bulb E F and intervening tube, 
