
CORRECTION TO BAROMETER FOR FORCE OF WIND. 379 
that every gust of wind was indicated by a corresponding depression of the baro- 
meter, whilst the barometer on the open ground remained stationary during all 
the changes in the amount of pressures of the wind, whether arising from the in- 
creased force of the gale, or from the intermittent gusts. 
It was, therefore, obvious that the cause of the depressions of the fiance 
was owing solely to the screened position of the instrument in the cottage and in 
the summer-house ; and that all barometers in detached houses, or observatories in 
exposed situations, must be similarly affected; and that a ship’s barometer, which 
is always hung in the cabin, and therefore also in a screened position, must be 
affected in a like manner. 
The cause of this phenomenon may be explained by the pneumatic experiments 
made by Hawkessee and Lestie, and by the hydrodynamic experiments of Brr- 
NOUILLI and VENTURI, though the former were made to illustrate a different sub- 
ject from that which is now under investigation.* 
“ Dr Hauiey sought to account for the depression of the barometer before a 
storm, to the withdrawing of the vertical pressure of the atmosphere, when borne 
swiftly along the surface of the globe by a horizontal motion.”—Encyc. Brit. 
The experiment of HAwWKESBEE was made with the view of illustrating and 
supporting the above hypothesis, whilst the experiment of Leste was made with 
the view of refuting it; but they each serve admirably to explain the cause of 
the depressions of the barometer in a screened position during a gale of wind. 
In HAWKESBEE’s experiment, two barometers are enclosed in boxes which are 
Fig. 2. 





















connected by a pipe, as shewn in the wood-cut. A globe of compressed air is 
screwed to a tube leading horizontally into the upper part of one of the boxes, 
whilst a larger tube is placed opposite to it, for the escape of the air. When the 
* I am indebted to my friends Professor Kennanp and Professor-Piazzi Smytu, for drawing 
my attention to these experiments. 
