310 Mr R. Adie's Description of a new Anemometer. 



changes. Most anemometers hitherto constructed measure the 

 velocity of the wind by its mechanical effects ; on the principal 

 of exposing a surface of known extent, or sails moving on an 

 axis, to its action, the force or pressure on the surface being 

 measured by the compression of a spring or air bag, by raising a 

 column of fluid, or by the elevation of a weight round an axis 

 acting on the arm of a variable lever ; thereby balancing, and 

 consequently measuring, the force of the wind. But to all of 

 these methods there are objections. To the spring, which is 

 the most simple, from its change of strength by change of tem- 

 perature, and from the change of elasticity by frequent com- 

 pression, and to all from the difficulty of maintaining the sur- 

 face at all times perpendicular to the direction of the wind. The 

 anemometer, or wind-gauge invented by Dr Lind, and by which 

 the greatest number of observations with which I am acquainted 

 have been made, is free from most of those objections, but in 

 this instrument the scale is so minute, that small changes or 

 light currents of air are not easily perceptible. I shall not, 

 however, take up the time of the Society by entering farther in- 

 to the merits of the different anemometers that have been pro- 

 posed, but proceed to lay before you the description of an in- 

 strument which was designed and constructed by Mr R. Adie 

 about two years ago. 



The instrument consists of a light cylindrical vessel, made of 

 thin copper, close and air-tight at one end, the other being open. 

 This cylinder is placed, inverted, within another of greater dia- 

 meter, filled with water; one end of a tube is made to pass 

 through the bottom of the outer cylinder, and to terminate above 

 the surface of the water, the other is carried into a free and ex- 

 posed situation ; on the top of this tube is placed a chamber, ha- 

 ving a funnel-mouth, moveable round the tube, and it is made 

 air-tight by a mercury valve. The opening is kept exposed to 

 the perpendicular action of the wind by means of a vane placed 

 opposite and attached to it. Over the end of the tube which 

 passes through the water, the inner cylinder is suspended by a 

 cord passing over a wheel, placed on an axis above, its open 

 end passing into the water. If now a current of air be allowed 

 to pass down the tube its effect will be to force up the cylinder 



