136 -REPORT—1846., 
posterior slope W w, fig. 1, has passed, and the posterior trough w, fig. 1, now 
occupies the line in which the anterior trough extended. 
From these considerations, we readily see that the wave is a convenient 
method of representing the barometric fluctuations; we have already noticed 
the wave motion, the lateral transference of the parallel beds of aérial currents. 
We have seen that the rise is due to the anterior slope and the fall to the 
posterior ; and we now further learn that the direction of the aérial current on 
the anterior slope is at right angles to the axis of translation directed towards 
the left-hand, while on the posterior slope it is the reverse; still at right angles 
to the axis of translation, but directed towards the right-hand. 
Having thus noticed the wave-motion with its accompanying ai-motion, 
these interesting questions suggest themselves. How are the forces of this 
air-motion arranged? Jo all the particles move with the same velocity ? 
Are there different velocities in different parts of the wave? Our anemo- 
meters will answer these questions. In the troughs, the edges 6 6 aa, the 
forces are strongest; as the barometer rises, the force gradually subsides; when 
the crest passes, it is zero; and as the barometer falls, it increases until the 
trough passes, when it is again strongest. 
The examination of the transit of a single wave by means of barometric 
and anemonal observations, would be comparatively easy, but it seldom 
happens, from the operation of natural causes, that an isclated or solitary 
wave is produced. In almost every instance (except in those in which the 
generating power is very much greater than any which occasions the pro- 
duction of smaller waves) the wave is contemporaneous with others of equal, 
if not of greater magnitude, so that different systems are in motion at the 
same time, each individual pursuing its own course, and although perfectly 
independent of every other, yet greatly modifying the resulting phenomena 
as exhibited by the barometer and anemometer. When therefore we pro- 
ceed with the examination of certain barometric and anemonal phenomena 
in the manner above alluded to, we are speedily perplexed with the baro- 
metric and anemonal effects of cross waves; the flowing of one set of waves 
in a certain direction is apparently interrupted and interfered with by an- 
other in a different direction, and before the first set can be exhibited with 
its proper proportions, and the true altitudes, amplitudes, velocities, and direc- 
tions of its individual waves assigned, all the phenomena of the other set 
must be carefully disentangled and separated from the aggregate phenomena 
presented by the contemporaneous systems. The barometric curve, including 
a complete rise and fall at any one station, is not the curve resulting from 
the transit of any one wave; it does not represent the form of any reality 
in nature ; but it does represent, and is an exponent of the effects resulting 
from the contemporaneous transits of waves, or systems of waves, such as have 
been described. 
The contemporaneous existence of these cross waves, with their appro- 
priate aérial currents, as manifested by the barometer and anemometer, ap- 
pears likely to form an experimentum crucis between the conflicting hypotheses, 
the oscillations of the barometer as dependent on waves, in contradistinction 
to that of the same oscillations as dependent only on the aérial currents. 
When a current meets with another at any angle, both are altered in direc- 
tion; and if the forces are different, the united current proceeds with an 
increased or diminished strength, according to the situation of the station 
relative to the separate currents before confluence. This union would of 
course influence the barometer; if the station is in a current of slow pro- 
gress, and the air possesses considerable density, the barometer would fall 
upon the new current being established ; while at another station, where the 
force of the wind is great and the pressure low, it would rise when the con- 
