62 REPORT—1845. 
flow are shifting ones, the same station will necessarily be oftener in a south- 
erly than in a northerly current (in the northern hemisphere), and the pro- 
portion of southerly wind will in the course of the year exceed that of north- 
erly. Moreover the southerly winds bring with them a quantity of vapour, 
with which they are continually parting in the form of rain and other preci- 
pitations: the returning northern dry winds do indeed bring back the same 
mass of air, but without its aériform companion, which having now assumed 
the form of liquid, no longer contributes to raise the column of mercury in the 
barometer, On considering the above-described alterations to which the at- 
mosphere is subjected on its passage from and return to the equator, we see 
that throughout the temperate zones the mean direetion of the wind may be 
from the equator, converted by the rotation of the earth into a south-westerly 
direction in the northern, and a north-westerly in the southern hemisphere. It 
is plain, however, that taking the year in detached parts, the air may be flowing 
towards the pole in one place and towards the equator in another: and we do 
find that in summer the direction of the wind in North America is relatively 
more southerly than in winter; whilst the contrary is the case at the same 
season in Europe. To arrive at decided conclusions, however, on this point, 
we require simultaneous observations, and on account of the great variability, 
the full record of the direction and pressure of the wind. 
If 6, 6, b, b, . . . . b, denote the mean height of the barometer respect- 
ively for the winds S., S.W., W.,. ...S.E., 2, 2 .... 2%, the number of 
the observed directions, then the mean height of the barometer b will be 
— 114) + Me by + ty by ores + tg by 
MR, + My +My 220. + Mg 
If all the winds had blown with equal frequency, the direction of the wind 
would have had no influence on the mean height of the barometer. If, then, 
b,+6,+ b5..+.+0% 
8 
Thus the difference 6 — 5’ gives the influence of the mean direction of the 
wind on the mean height of the barometer. If we thus possess a barometrie 
wind-rose, we are enabled to decide whether the mean pressure is in this way 
normal or anomalous. The same holds good for temperature and moisture. 
But such calculations require the directions of the wind to be given as fully 
as the corresponding readings of the other instruments. No matter whether 
the result be to find a material influence or not, for progress is equally made 
by a proposed possible explanation being set aside as insufficient, or by its 
being justified and confirmed. The taking in determinations of intensity 
alters the problem. Hitherto we have regarded as the mean temperature of 
a place, the arithmetical mean of observations at equal and short intervals 
during the period under consideration. But inasmuch as when the wind 
blows strongly more air passes over the place of observation than when the 
eurrent is slower, the number which should give the mean temperature of the 
air flowing over the station may differ from that which is given by the arith- 
metical mean of the observations. It is not improbable that in certain meteo- 
rological questions these hitherto unconsidered values may be those treated 
of, and hence even an approximate measure of intensity may be an im- 
portant contribution; in this case also every measurement of intensity must 
be combined with the corresponding barometric, thermic and hygrometric 
record. 
These observations will also determine the important question, whether, in_ 
the horizontal movement of the atmosphere, we are to separate the dry air 
n, = N,=N,.-...=%,, the barometric height b’= 
