248 
SECOND REPORT— 1832 . 
by the wind itself, I proposed that small spherules of wood or 
other light matter, or even shot, should be let fall through a free 
space, suppose of three feet, and that the force and direction of 
the wind should at once be measured, at every interval of the 
falling of a spherule, by the amount and direction of the de¬ 
flexion produced, and which should be ascertained by the divi¬ 
ding into compartments a platform arranged to receive them. 
I have made some experiments on the subject, and have 
every reason to believe that the method admits of great accu¬ 
racy, and that it is perhaps the most satisfactory mechanical 
one that has been proposed. I conceive that Professor Leslie’s 
ingenious plan of measuring the force of the wind by the cooling 
of a thermometer exposed to it, is the most satisfactory indirect 
method, and has not met with the attention which it deserves*. 
We have seen that the direction of the winds exerts an impor¬ 
tant influence on the height of the barometer. There is another 
source of action which it creates, and which is less understood. 
M. Schubler has shown, in an interesting paper, that the winds 
have each their characteristic electric power. The precipita¬ 
tions during the winds from the northern half of the circle of 
azimuth, have a ratio of positive to negative electricity which 
is a maximum ; and in the other half it is a minimum, the nega¬ 
tive precipitations when the wind is south being more than 
double the positive ones. The mean intensity of electricity, 
independent of its sign, is greatest in north winds. We must 
refer to M. Schubler’s paper for his reasoning upon these 
facts +. 
It is a fact to be attended to, that the progress of a wind and 
the storm which may accompany it is not always in the direc¬ 
tion in which it blows. M. Pouillet terms the modes of propa¬ 
gation of wind by “ impulsion ” and by “ aspiration J.” In the 
latter case, a vacuum or diminution of pressure being at any 
point effected, the air which flows to fill it up commences, of 
course, its motion nearest the point of deficient equilibrium, 
from which the current gradually retires. Franklin long ago 
compared it to the flow of water through a canal upon opening 
a sluice. Mr. Mitehel in America has discussed this view 
of Franklin, which he thinks w r ill not always apply; indeed 
the case is one of difficulty, and, unless we can ascend to 
the first active causes, would only lead into unprofitable specu¬ 
lation. In many cases the deficiency assumed on Franklin’s 
hypothesis cannot be proved, and in some is untenable ; but w r e 
* Essay on Heat , p. 284. 
f Jahrbuch der Chemle and PhysiJc, 1829, Heft iii.; Bibliotheque Univer- 
selle, Nov. 1829; Edinb. Journal of Science, N.S. iii. 116. 
J Elemens de Physique, ii. 715. 
