Ixxxvi GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
180. Differences of the Daily Mean Temperature from the Monthly Means.—From the means of the results 
for the four years 1843-6 in the last line of Table 74, the differences of the daily mean temperature from the 
monthly mean temperature are greatest in the six months October to March, and they are least in the remain- 
ing six months; there are irregularities in the value of the mean difference from month to month; the mean 
difference is less in December than in the immediately preceding and succeeding months, and it has nearly the 
same value as in June. The mean difference is greatest in January, and it is least in August. From the four 
years’ observations the mean temperature of a civil day differs on the average 3°6 from the mean tempera- 
ture for the corresponding month. 
181. The irregularity of the monthly mean temperature does not seem to be connected with that of the 
daily mean temperature; thus, March and October, which have the least variation of monthly mean tempera- 
ture, have the greatest variation of daily mean temperature, with the exception of January. 
182. Diurnal Variation of Temperature.—Table 75 has been formed in the manner already described for 
Table 12. The approximate epochs deduced from Table 75 are given in Table 76. 
TABLE 75.—Diurnal Variation of the Temperature of the Air for each Astronomical Season and for 
the Year, deduced from the Observations of the Years 1843-6. 
Intervals, 
Maximum 
P.M. .M. .M. p.M. Mean| A.M. Mean| Minimum 
to to to 
Maximum,|P.M. Mean.) Sunrise. 
Noy. Dee. Jan. 
Feb. Mar. Apr. 
May June July 
Aug. Sept. Oct. 
Year 
The following are the conclusions from the previous table :— 
1st, The minimum temperature occurs immediately before sunrise in summer, about 13 hours before it in 
winter and spring, and about half-an-hour before sunrise in autumn; it is evident, however, that accuracy 
in the determination of the interval is not increased by combining several months together, since, in the result 
for the year, the minimum appears to occur at a greater interval from sunrise than in any of the quarters. 
2d, The maximum temperature occurs latest after noon before the autumnal and after the vernal equinox ; 
it occurs nearest noon in summer, but the temperature changes very slowly in that quarter from 1" to 3" p.m. 
