34 



LANDER^S ANEMOMETER. 



Patent Oj>j>Ue<l for. 



This Anemometer is an instrument in which the wind blowing against the open mouth of a tube, 

 which is kept facing the wind, exerts a pressure which is conducted down a tube or series of tubes 

 fixed together by unions and thence by means of a mercury joint and flexible tubing to the 

 interior of a thin bellows so delicately counterpoised that it rises with the faintest breeze. Attached 

 to the disc or plate of the bellows is a lever carrying a pen which records on a drum revolved by 

 clockwork. The levei is weighted by means of a small conical piece of hard wood or composition, 

 which floats in a vessel of glycerine, the density of which is adjusted to allow the float to 

 almost sink. When the float thus lies in the glycerine it has no weight, but when lifted up by the 

 wind the weiglit gradually increases until it is lifted completely above the surface of the liquid. 



The effective area of the disc or plate acted upon and lifted by the wind inside the bellows is 

 about 1-iiOth of a square foot, and according to the official table of the British Meteorological Office 

 this surface would lift a ooz. weight in a gale force 9, but a lighter weight nearer the pen would be 

 equal to .'ozs. on the centre of the bellows, and the point from which the weight is suspended being 

 twice as far from the hinge as the centre of the bellows, it follows that a 2.\oz. weight here is equal to 

 oozs. placed exactly on the centre of the disc. The pen is again double this distance, and therefore 

 moves twice as much as the weight. Below is given a summary of the official table from which it is 

 easy to calculate the weight lifted by wind of any force, viz. : By dividing the number of ounces by 200. 



By cnstricting the tube by means of a clamp, one can get a record of mean sustained pressure, 

 quite unlike the record obtained with the open tube which shows every single puff of wind, however 

 sudden and momentary. 



The size of the scale can be varied by using a float of smaller or greater weight, or by placing the 

 float nearer to or further from the pen. 



I'he lower end of the tube near the mercury joint is removable and^is wrapped around with a chart 

 on which is recorded tlie direction of the wind by means of a pen which is allowed to slowly slide down 

 a brass bar at the same rate as the drum revolves with the pressure record. 



Before use the bellows is carefully tested by conducting a branch of the wind pressure to one end 

 of a U shaped tube filled with turpentine, and as a difference of level cf one foot with this liquid 

 represents a pressuie of Solb?., it is from the same table eaey to calculate the difference of level for 

 wind of any force. 



