1821.] Col. Beaufoy on a new Wind Guage. 431 



Article VII. 



Description of a new Wind Guage, or Apparatus, for determining 

 the effective Pressure of the Wind upon a given Surface. By 

 Col. Beaufoy, FRS. '(With a Plate.) 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, Bushcy Heath, near Stanmorc, Xov. 18, 1821. 



I have the pleasure of sending a drawing and description of 

 a new anemometer, which I find from experience is capable of 

 measuring the momentum of the wind with great accuracy. 



Several instruments of this kind have already been constructed 

 with more or less skill ; but as the generality give merely the 

 relative impulse, I shall only notice three of the best. 



The first was invented by Mons. Bouguer, and is fully 

 described in his learned and scientific " Traite du Navire, de sa 

 Construction et deses Mouvemens," published in the year 1746. 

 The second was constructed by Dr. Burton, and its machinery 

 is detailed in Mr. Martin's second volume, p. 211, of the Philo- 

 sophica Britannica. The third is that of Dr. Lind, an account 

 of which is to be found in Dr. Mutton's Mathematical Dic- 

 tionary. M. Bouguer's instrument is exceedingly well adapted 

 for making experiments at sea ; but I found it could be rendered 

 more accurate by cutting teeth in the slider to turn wheel-work, 

 to which hands were attached similar to those in the accompany- 

 ing plate. The anemometer of Dr. Burton shows only the rela- 

 tive impulse ; but the absolute force of the wind may be deter- 

 mined by referring to p. 94, vol. viii. of the Annals. The 

 disadvantage of Dr. Lind's wind guage is, that in stormy weather, 

 the water is liable to be blown out of the tube. It was with the 

 machine I am now about to describe, that some of the experi- 

 ments were made recorded in p. 277, vol. vi. of the Annals. 



I remain, dear Sir, truly yours, 



Mark Beaufoy. 



The apparatus consists of a thin board or screen, one foot 

 square, having a brass bar projecting perpendicularly from its 

 back surface in the middle thereof; this bar is supported and 

 guided between eight brass rollers, arranged in a fixed frame in 

 such manner that the bar and screen may be capable of sliding 

 freely backwards and forwards, by the action of the wind upon 

 the surface of the screen, when the apparatus is placed with the 

 bar in a horizontal position. The force with which the wind 

 acts upon the screen is ascertained by a weight suspended by a 

 silken cord passing round a spiral or fusee ; upon the axis of 

 which, a small cylindrical barrel is fixed having a chain (similar 

 to those used in clocks) winding upon it ; the other end of the 

 chain is attached to the sliding bar, so that when the screen is 



