sudden.

Standing on an open heath on a gusty day, we may often note the rhythmic
buffeting of the wind, resembling the assault of rolling billows of
air. The evidence of these billows has been actually traced far aloft in
balloon travel, when aeronauts, looking down on a wind-swept surface of
cloud, have observed this surface to be thrown into a series of rolls
of vapour, which were but vast and veritable waves of air. The interval
between successive crests of these waves has on one occasion been
estimated at approximately half a mile. We have seen how these air
streams sometimes hold wide and independent sway at different levels.
We have seen, too, how they sometimes meet and mingle, not infrequently
attended with electrical disturbance

Through broad drifts of air minor air streams would seem often literally
to "thread" their way, breaking up into filaments or wandering rills of
air. In the voyage across Salisbury Plain lately described, while the
balloon was being carried with the more sluggish current, a number of
small parachutes were dropped out at frequent intervals and carefully
watched. These would commonly attend the balloon for a little while,
until, getting into some minor air stream, they would suddenly and
rapidly diverge at such wide angles as to suggest that crossing our
actual course there were side paths, down which the smaller bodies
became wafted.

On another occasion the writer met with strongly marked and altogether
exceptional evidence of the vehemence and persistence of these minor
aerial streamlets. It was on an occasion in April weather, when a heavy
overcast sky blotted out the upper heavens. In the cloud levels the wind
was somewhat sluggish, and for an hour we travelled at an average speed
of a little over twenty miles an hour, never higher than 3,000 feet.
At this point, while flying over Hertfordshire, we threw out sufficient
ballast to cause the balloon to rise clear of the hazy lower air, and
coming under the full influence of the sun, then in the meridian, we
shot upwards at considerable speed, and soon attained an altitude of
three miles. But for a considerable portion of this climb--while, in
fact, we were ascending through little less than a mile of our upward
course--we were assailed by impetuous cross currents, which whistled
through car and rigging and smote us fairly on the cheek. It was
altogether a novel experience, and the more remarkable from the fact
that our main onward