100 
Velocity of the Wind. 
current testimony of several series of well conducted experiments, I hope to excite 
those who have a zeal for science, and particularly for the branches connected with 
their profession, to follow up the subject, and give the “ Scientific Gleaner," the ho- 
nour of establishing upon a surer basis, the laws of aerial motion and force. 
The usual machines constructed for the purpose of measuring the velocity of the 
wind, are essentially faulty in principle ; for they depend upon the measurement of 
the force exerted by the moving air upon a given surface, and the connection between 
these two properties is only assumed theoretically. In the course of a voyage from 
England, I registered daily the indications of an instrument on this principle, one 
which exposed a surface of six square inches perpendicularly to the action of the 
current ; but, I soon began to doubt the accuracy of its indications, and to wish 
for an instrument capable of measuring directly the velocity itself. 
With this view, I adapted a sort of small windmill to a train of watchwork, so as 
to register the number of revolutions made in a given time ; the friction opposed 
hardly any resistance to the turning of the vanes, so that it might be judged before- 
hand, (as it afterwards proved,) that the number of rotations would be proportional 
to the velocity of the wind. This instrument had the additional advantage of not be- 
ing aflected by sudden gusts and irregularities, and of being exposed to the free cur- 
rent at the end of a long staff, whereas the common anemometers must be held near 
the eye, and are then difficult to read off from their continual vacillations. 
The problem of determining the number of revolutions of the windmill which 
corresponded with given velocities of wind was necessarily left to be solved on terra 
firms ; and the method pursued does not, 1 think, admit" of cavil, as it will readily 
be granted that it is the same thing whether the instrument move through the air, 
or the air move past the instrument, the velocities beifig always equal. 
The windmill then, furnished with a proper trigger to stop or set it in motion at 
given signals, was attached to the end of a long, wooden arm branching out from an 
upright axis, to which various degrees of rotatory force were imparted. The instru- 
ment thus described a circumference of such magnitude that, ns regarded its own 
size, it might be considered a. straight line. 
The air of the apartment was also perfectly calm and undisturbed. It required a 
motion of 2i feet per second or one and half miles per hour, to overcome the friction 
of the machinery. The .following table embraces the results deduced from the ex- 
periments, and shows that the revolutions arc almost exactly in the ratio of the velo- 
cities, the only deviations being at both extremes, as might have been anticipated. 
Velocity of the Wind. 
Feet per minute. 
Miles per hour. 
Revolutions of mill 
anemometer. 
3 
2.02 
120 
4 
2.75 
250 
5 
3.4 
375 
6 
4.05 
500 
7 
4.8 
615 
8 
5.45 
730 
9 
6.1 
845 
10 
6.85 
960 
ii 
7.5 
1075 
12 
8.15 
1190 
13 
8.9 
1305 
14 
9.55 
1410 
15 
Tt r.vn... • 
10.25 
1505 
Difference. , 
130 
125 
125 
115 
115 
115 
115 
115 
115 
115 
105 
95 
- im-ici v mi up trom nonce t ie numbers u . ,v. 
wind upon a i e L, * T “ Sn > < ? med taMe > force of the 
common tables thereof The Hff Ztl ’ *3 i “l 0 . .according to the 
miles is also infcSdi ^ Thc shi P' s ^ in 
sail she carried aUhe iiZ y g " BUt 1 ° mltted to note «> quantity of 
