METEOROLOGICAL INSTRUMENTS. 145 



kneed or bent perpendicularly outwards, and has its mouth 

 open towards F ; on the other leg, c D, is a cover, with a 

 round hole, G, in the upper part of it, two-tenths of an inch 

 in diameter. This cover and the kneed tube are connected 

 together by a slip of brass, cd, which strengthens the whole 

 instrument, and serves to hold the scale, H i. The kneed 

 tube and cover are fixed on with hard cement, or sealing- 

 wax. To the same tube is soldered a piece of brass, e, with 

 a round hole in it to receive the steel spindle, K L, and at 

 /another such piece of brass is soldered to the brass hoop, 

 g k, which surrounds both legs of the instrument. There is 

 a small shoulder on the spindle at/, upon which the instru- 

 ment rests, and a small nut, i, to prevent it from being 

 blown off the spindle by the wind. The whole instrument 

 is easily turned round upon the spindle by the wind, so as 

 always to present the mouth of the kneed tube toward* it. 

 At the end of the spindle there is a screw, by which it may 

 be screwed to the top of a post or stand ; it has also a hole 

 at L, to admit of a small lever for screwing it into wood 

 with greater facility. A thin plate of brass, k, is soldered 

 on the kneed tube, about half an inch above the round hole 

 (f, so as to prevent rain from falling into it. 



This instrument serves to ascertain the force of the wind, 

 by filling the tube half full of water, and pushing the scale 

 a little up or down, till upon the scale, when the instru- 

 ment is held perpendicularly, be on a line with the surface 

 of the water, in both legs of the wind-gauge. The instru- 

 ment being thus adjusted, hold it up perpendicularly, and 

 turning the mouth of the kneed tube towards the wind, ob- 

 serve how much the water is depressed by it in one leg, and 

 how much it is raised in the other. The sum of the two is 

 the height of a column of water, which the wind is capable 

 of sustaining at that time ; and every body that is opposed 

 to that wind, will be pressed upon by a force equal to the 

 weight of a column of water, having its base equal to the 

 surface that is opposed, and its height equal to the altitude 

 of the column of water sustained by the wind in the wind- 

 gauge. Hence the force of the wind upon any body, where 

 the surface opposed to it is known, may be easily found ; and 

 ready comparison may be made betwixt the strength of one 

 gale of wind and that of another, by knowing the heights 

 of the columns of water which the different winds were ca- 



VOL. H. 13 



