284 ABSTRACTS ‘OF THE MAKERSTOUN OBSERVATIONS, 1843. 
Mean Meteorological Seasons. 
Spring, The maximum between 9" p.m, and 5% a.m. The minimum at 3" 30™ p.m. 
ree ries maximum before 5" a.m. A secondary minimum about 2" p.m. 
| A secondary maximum about 3" 20™ p.m. The minimum about 5" p.m. 
Autumn, The maximum between 9" p.m. and 5° a.m. The minimum about 1" 40™ p.a. 
Winter { The maximum after 9% pm. The minimum before 5" a.m. 
> | A maximum at 9" 40™ a.m. A minimum at 2" 20™ p.m. 
Astronomical Seasons. 
Sains rg maximum after 9° pv. A minimum before 5" a.m. 
pring, A maximum at 82 10™ a.m. The minimum at 2 40™ p.m. 
Summer, The maximum before 5" a.m. The minimum at 45 40™ p.m. 
Autumn, The maximum before 5" a.m. The minimum about 4> 20™ p.m. 
Winter ee maximum after 9" p.m. The minimum before 5" a.m. 
> | A maximum at 9" 40™ am. A minimum at 1 40™ p.m. 
The diurnal variation for the year 1843 gives— 
The maximum between 9 p.m. and 5 a.m. 
The minimum at 3" 20™ p.m. 
The division, then, of the total pressure of the atmosphere into two paris, namely, the dry air and aqueous 
vapour, indicates only a single maximum and minimum in the diurnal curve for the year (as has been shewn 
by M. Dove and Colonel Sasryz). The minimum pressure of dry air takes place nearly two hours after the 
maximum temperature. We have still the double maximum and minimum in the Winter months. Why are 
both exhibited in the pressure of the dry air in Winter? We have seén that the diurnal range of the aqueous 
vapour follows, to some extent, the diurnal range of temperature, and that it is greater im Summer than in 
Winter. We have also seen that, for the year 1843, the diurnal variation of the total atmospheric pressure 
has a greater range in Winter than in Summer. It scems curious that the diurnal range of total pressure 
should diminish when the ranges of its two components increase, and that, when the diurnal ranges of the two 
components diminish, the diurnal range of the compound pressure should increase. There is no difficulty in 
seeing, even if the theory be at fault, or if the pressure of aqueous vapour be inaccurately determined, that 
the comparatively great diurnal range of aqueous vapour pressure for the summer months, and for the year, 
will swamp the smaller range of the total pressure, and produce a curve for the dry air, with a single maximum 
and minimum, inverse to that for the pressure of aqueous vapour. The fact that, when the diurnal range of 
the aqueous vapour pressure is least, namely, in Winter, the diurnal range of the total pressure is greatest, 
and the double maximum and minimum most distinctly marked both for the assumed dry air and total pres- 
sures, leave this mode of resolution with its original difficulties. 
It was pointed out, Table XI., that a secondary maximum and minimum of the pressure of aqueous 
vapour occurred in several months about 1", 3", and 5" p.m. No such periods were observed for the humidity 
or total atmospheric pressure. Of course, then, in assuming the total pressure to be composed of the pressures 
of dry air and of aqueous vapour (as calculated), we may expect to find the dry air accommodating itself to the 
calculated vapour pressure. Accordingly, as has been noticed above, secondary minima and maxima of dry 
air oceur at the same times as the secondary maxima and minima of aqueous vapour. ‘This does not seem 
very probable. 
heh ad 
