64 _ Meteorological Observations. 
this to the first mean, and divide the sum by 2, for the meat 
of the whole month—which enter accordingly. __ 
As the method which is now prescribed for making obser-" 
vations by the thermometer, and deducing their results, differs 
from the usual practice, it is proper to give the reasons for its 
adopti 
Phe most obvious method for finding the mean temperature 
sum of the Bhi by their number. But this cannot be 
the thermometer rises and falls on each day, and to take it-foe. 
granted, that if the observations were made at every hour, 
from one extreme to the other, they would give a series oF 
numbers in arithmetical progression, the sum of which, divid- 
ed by the number of observations, or its equal, half the sum of 
the extremes, would then give the mean. For example, sup- 
pose the cones degree of the thermometer to be 30, at 6 
o'clock in the morning of any days’ and the highest degree 
48, at 3.o'clock in the the afternoon ; these, with the eight inter- 
mediate hours, will give “a-series of 10 terms, 30 and 48 being 
the extr extremes : then — 
30+ 48 x 10 
== 390, the series; this, divided by 10, the num- 
Davart tree sper of cheepvation’y Will. give 
30+ 48 © ; 
-39 for ae mean, hats is, "hair the sum of the extremes, 
2 . Again, suppose on the morning of the next day, 
the extreme depression to be 32 degrees, then, for the time 
between the afternoon observation and that of the next morn- 
whole day, dle ons the time 
pan orang obra arte fe for ee the mean 
i onc ston. lhe Bex ¢ . 
the c mornings 
observation Hy: the i s ant divide th b 
ee ays, e — ye 4, thus. 
“Sgt 39,5. 
