220 Proceedings of the Royal Society 
place, they are accompanied by a rise of the barometer. The 
mode in which these N.E. surface winds are enabled to overcome 
the effect of friction, and to accumulate on the surface, may be 
thus explained. They are cold and dense, and they enter under- 
neath a milder atmosphere in the form of a wedge and raise it above 
them. To enable them to do this they must have a copious source 
of supply from an area of high pressure, and they are also aided 
generally by descending currents, which possess a great amount of 
potential energy. 
As is well-known by seamen, these surface U.E. winds appear 
with a remarkable amount of suddenness and violence, and the 
disasters which accompany them have been often recorded. South- 
west gales which blow aloft approach much more slowly, and, as 
this approach is first exhibited aloft, they can be predicted with 
much certainty. 
In the last paper just alluded to it was mentioned that the range 
of the thermometer is equally great both above and below its mean. 
But with the barometer, the extent of its range above the mean 
is not more than one-half of that which takes place when it is below 
it. When it is below the mean, Equatorial winds generally prevail, 
such as those S.W. just alluded to, which are accompanied by 
removal and lifting. When above the mean, Polar winds and calms 
prevail, which are not accompanied by removal and lifting. Hence, 
as a general rule, Equatorial winds exhibit an amount of fictitious 
pressure, while Polar winds show more nearly, real or statical 
pressure, which, however, may possibly be so much in excess. 
Much important information as to the mobility of the upper aerial 
strata may be shown by the experiments made by Professor 
Tyndall at Chamouni, and at the summit of Mount Blanc. 
Erom observations made by the late Mr Johnson, director of the 
Oxford University Observatory, it was found that, at a height of 
110 feet from the ground, the velocity of the wind was found to 
be 2J times that indicated by an instrument at 22 feet above 
the soil. This velocity, of course, increases with the elevation, 
and to the extent of five or six fold, as shown by Glaisher. In 
the address of the President, H. S. Eaton, on 21st Eebruary 
1877, he alludes to the ascent of a balloon from Paris. At an 
elevation of 6560 feet, a violent wind was encountered, and on 
