222 DOVE ON THE NON-PERIODIC VARIATIONS IN THE 
entire atmospheric pressure might be attributed to the elasticity 
of the aqueous vapour in different latitudes. The facts of obser- 
vation, extending over several years, are still too isolated to per- 
mit more than an approximate connexion to be traced. 
In searching for the laws which regulate the periodic variations, 
two modes have been pursued, a practical and a theoretical one ; 
by the first, methods are sought by which the mean state of the 
atmosphere may be calculated ; and by the second, the causes of 
the changes are examined. 
In considering the daily variations of temperature, the first 
alone has been employed, while it is allowed that the second 
method is very important as regards the barometrical and hy- 
grometrical variations (Vide Dove on the Daily Oscillations of 
the Barometer). I have endeavoured to show that the whole of 
the non-periodic variations may be referred to, and explained by, 
one primary principle, which I have called the “ Law of Rotation” 
of the winds. Aristotle observed the regular passage of the dif- 
ferent winds into each other : Von Buch proved the influence of 
the direction of the wind on the barometer, thermometer, and 
hygrometer. Now, as the greater number of the so-called irre- 
gular variations of the instruments are only the passage of the 
barometric, thermic and hygrometric states of the winds into 
each other, it is clear that the laws of the irregular changes can 
only be recognised when the mean variations of the direction of 
the wind are combined with the mean distribution of pressure, 
temperature and moisture in the wind-rose (Wind-rose). By com- 
paring the direction of the wind with the state of the three in- 
struments for Paris and London, I obtained exactly the same re- 
sults as I had formerly at Konigsberg; the circle of the wind- 
rose may be divided into halves; if the instruments rise on 
one side, they fall on the other,—the two parts exhibit exactly 
opposite phenomena. It was then easy to refer the whole of the 
phznomena of the weather to the conflict of two winds, whose 
direction agrees with the dividing line of the wind-rose, and which, 
when acting singly, produce the extremes; and when only par- 
tially prevailing, either over the other, cause those changes which 
distinguish our climate. Howard calls these winds the true 
monsoons of our regions. 
If, as Hadley has done, we consider the difference in the ra- 
pidity of rotation of the earth in different degrees of latitude as _ 
a cause affecting the currents of air, and if we moreover intro- 
