128 
MR. GLAISHER ON THE CORRECTIONS TO BE 
The diurnal oscillations of the sum of the pressures of air and vapour are plainly 
very different at different times of the year, the season therefore has an influence 
over the diurnal oscillation ; this circumstance is sufficient to prevent us from being 
able to determine the mean height by taking the observations at any fixed time 
throughout the year for the morning mean, and at any fixed time for the evening 
mean. That mean reading takes place with the greatest degree of steadiness, which 
occurs between midday and 2 ^ p.m. ; the actual time however varies with the season. 
As we can deduce the mean temperature of the air from a few daily observations, 
to be spoken of presently, so also can we deduce the mean reading of the barometer 
from a few readings taken daily ; and if this be the only element of investigation, that 
time or times most convenient to the observer may be chosen ; but if, in addition, such 
observations be needed as will serve for studying the irregular oscillations of the 
readings of the barometer, then several observations should be taken daily, and at 
such times as appear in the foregoing table to require the largest corrections, both plus 
and minus. The greater number of observations which are taken daily, will not only 
serve for investigations of irregular oscillation, but the mean pressure will be more ac- 
curately determined, and they will be available in the study of the transmission of waves. 
Table II. — Showing the corrections to be applied to the Monthly Mean reading of a 
thermometer placed at the height of four feet above the soil with its bulb freely 
exposed to the air, but in other respects protected from the influence of radiation 
and rain, at any hour, to deduce the true mean temperature of the air for the 
month from the observations taken at that hour. 
Local mean 
time. 
January. 
Feb. 
March. 
April. 
May. 
June. 
July. 
August. 
Sept. 
Oct. 
Nov. 
Dec. 
Midnight. 
O 
+ 1-0 
+ 1-6 
+ 2-9 
+ 4-8 
+ 5-4 
+ 6-2 
-1-3-0 
O 
+ 5-1 
+ 4-0 
+ 2-9 
O 
+ 1*7 
+ 6*9 
1 A.M. 
+ 0-9 
-t-1-8 
+ 3-0 
+ 5-2 
+ 6-0 
+ 7-1 
+ 5-5 
+ 5-5 
+ 4-3 
+ 3*0 
+ 1-8 
+ 1-0 
2 
+ 1-2 
+ 2-0 
+ 3-3 
+5-7 
+ 6-4 
+ 8-0 
+ 6-0 
-h6-0 
-t-5-3 
+ 3-4 
+ 2-0 
+ 1-2 
3 
+ 1-3 
+ 2-1 
+ 3-6 
+ 6-2 
+ 6-7 
+ 8-7 
+ 6*4 
+ 6-3 
+ 6-4 
+ 3-6 
-h2-0 
+ 1-3 
4 
+ 1-6 
+ 2-3 
+ 3-9 
+ 6-6 
+ 6-7 
+ 9-3 
-|-6'6 
-1-6-5 
+ 6-6 
+ 3-8 
+ 2-1 
+ 1-4 
5 
+ 1-8 
+ 2-2 
+ 4-0 
+ 6-7 
+ 6-3 
+ 8-8 
+ 6-2 
-1-6'5 
+ 6-2 
+ 3-8 
+ 2-0 
+ 1-4 
6 
+ 1-9 
+ 2-3 
+ 3-9 
+ 6-0 
+ 4-8 
+ 6-4 
+ 4-5 
+ 5-5 
-I-5-3 
-I-3-3 
+ 1*9 
+ 1-4 
7 
+ 1-9 
+ 2*1 
+ 3-6 
-I-4-3 
+ 2-6 
+ 3-0 
+ 2-5 
+ 3*3 
+ 4-0 
+ 2-8 
+ 1-7 
+ 1*5 
8 
+ 1-5 
+ 1-6 
+ 2-5 
+ 2-0 
+ 0-5 
0-0 
0-0 
+ 0-9 
+ 2-1 
+ 1-6 
+ 1-0 
+ 1-3 
9 
+ 1-0 
+ 0-7 
+ 0-2 
-0-9 
— 2-0 
— 2-5 
-2-0 
-1-6 
-0-4 
0-0 
+ 0-4 
+ 0-9 
10 
+ 0-2 
-0-5 
-1-9 
— 3-2 
-4-0 
— 4-5 
-4-0 
-3-5 
— 3-0 
— 2-0 
-0*6 
0-0 
11 
— 1-3 
-2-1 
-3*5 
— 5-3 
— 5-5 
— 5-8 
— 5*4 
— 3-4 
— 3-0 
— 3-8 
-2-0 
-1-3 
Noon. 
-2-3 
-3-2 
-5-0 
-6-8 
-6*7 
-7-3 
-6-4 
—6-3 
-6-4 
— 5*1 
-3-1 
-2-1 
1 P..M. 
— 2-9 
-3-9 
-5*8 
-7-9 
-7-5 
-8-1 
-6-7 
-7-5 
-7-1 
— 3-3 
-3-3 
— 2-4 
2 
-3-0 
-3-9 
-5-8 
— 8-2 
-7-7 
-8-6 
-6*7 
-7-7 
-7*1 
-4-9 
-3-6 
-2-3 
3 
-2-5 
-3-6 
-5*5 
-7-7 
-7-3 
-8-4 
— 6*5 
-7-0 
-6-6 
-3-7 
-3*0 
-1*9 
4 
-1-9 
— 2-8 
-4-5 
-6-7 
-6-1 
-7-4 
-5-8 
-3-5 
— 3-3 
—2-8 
-2-1 
-1-3 
5 
-M 
-1-6 
— 3-3 
-5-4 
— 4-8 
-6-1 
-4-9 
-3-6 
— 4-2 
-1-7 
-1-2 
-0*8 
6 
-0*6 
-0-6 
-1-8 
— 3-5 
-3-0 
-4-5 
-3-3 
-2-0 
—2-3 
— 0*8 
-0-4 
-0-4 
7 
-0-3 
+ 0-3 
-0-4 
— M 
-1-0 
-2-4 
-1-5 
-0-5 
-0*6 
0-0 
+ 0-1 
-O-l 
8 
+ 0-1 
+ 0-6 
+ 0-9 
+ 0-7 
+ 0-9 
0-0 
+ 0*3 
+ 1-0 
+ 1-0 
+ 0-7 
+ 0-6 
+ 0-2 
9 
+ 0-4 
+ 1-0 
+ 1-7 
+ 2-0 
+ 2-3 
+ 1-8 
+ 1*9 
-I-2-4 
+ 1-8 
+ 1-3 
+ 1-0 
+ 0*4 
10 
+ 0-6 
+ 1-3 
+ 2*3 
+ 3-2 
+ 3-5 
+ 3*6 
+ 3*3 
+ 3-3 
+ 2-7 
+ 1-9 
+ 1-3 
+ 0-5 
11 
+ 0-7 
+ 1-5 
+ 2-6 
+ 4-1 
+ 4-5 
+ 5-0 
+ 4-2 
+ 4-3 
+ 3-4 
4 2-4 
+ 1-5 
+ 0*8 
The sign denotes that the number is to be added, and the sign — denotes that 
the number is to be subtracted. 
