Diurnal Meteorological Conditions at Kimherlcy. 143' 



Among other things it will be seen that n^ is greater than u^ 

 now. 



Table 15 shows the mean barometric pressm^e of the air, hour by 

 hour, in each month and for the year. Here again, as in Table 3, 

 the columns have been extended past the second midnight. The 

 increase or decrease of pressure from one hour to the next will be 

 the most easily followed in Table 16, where the increases are shown 

 as before in heavier type. The first and greater maximum is at IX., 

 the second is a little before XXIII. The respective rises to each of 

 these, from the preceding minima, occupy about six hours. The fall 

 of pressure from these maxima occupy some 7"5 and 4*5 hours respec- 

 tively. The morning maximum follows the sun ; it is some two hours 

 earlier at midsummer than it is at midwinter. The most rapid rate of 

 rise of pressure to the first maximum happens within an hour after 

 the temperature minimum at sunrise. The pressure maximum 

 happens within an hour after the most rapid rate of rise of tem- 

 perature. So far, then, we have probably a fairly direct solar 

 effect. 



The most rapid rate of fall of pressure happens shortly after noon 

 at midwinter ; but an hour or so later at midsummer. And, conse- 

 quently, the portions of the monthly curves of pressure variation 

 {not the curves of pressure) lying between the times of pressure 

 maximum and greatest hourly decrease of pressure are twice as steep 

 in winter as in summer. Hence it seems to be a logical performance 

 to assign the rate of decrease of pressure to the influence of the 

 primary, afternoon, minimum of pressure following, with some regu- 

 larity, four hours later. The primary minimum of pressure for the 

 year is shortly after XVI., the monthly hour changing from 3.30 p.m. 

 in June to 4.30 p.m. in December. The greater rate of increase of 

 pressure to the second maximum falls pretty regularly in the fourth 

 hour after minimum ; but there is very little indication of a monthly 

 variation in the time of the second maximum. Now there is nearly 

 a two-hours' difference between the times of sunset in June and 

 December. Therefore, since all the barometric phases, with the 

 exception of the primary maximum, vary by one hour only at most, 

 it seems to follow that these, with the one exception, have no close 

 affinities to the temperature changes in the lower air. We need not 

 claim this as a new suggestion. Hann, long ago, was " convinced 

 that attempts to explain the diurnal oscillation by means of the daily 

 variation at any one place will lead to no conclusions." He further 

 adds, "I am of opinion that the observed daily variation of wind 

 and temperature do not stand in as close a relation to the diurnal 

 barometric oscillation as has hitherto been assumed . . . for how 



