Fie. 3. 



130 Mr. T. Tate on a new Evaporameter and Absorbometer : 



lower extremity, for admitting the external 

 air into the tube as the water is being absorb- 

 ed by the absorbent e K, on which the tube 

 stands, thereby maintaining the water at a 

 constant pressure on the absorbent. The in- 

 strument is adjusted in the following man- 

 ner : — The tube is held in a vertical position, 

 with its mouth upwards, and filled with water; 

 the flat surface of the absorbent is then placed 

 on the orifice of the tube, and the whole is 

 inverted and placed upon the edge of the 

 table. In the case of flexible absorbents, 

 such as calico or cloth, the material is first 

 covered with a piece of polished slate, and 

 then the instrument is inverted as above described. 



A more delicate Evaporameter, answering the purpose of a 

 Hygrometer. 



This instrument is a modification of the apparatus represented 

 in diagram 2. The tube ABKE being filled with filtered rain- 

 water, a damp piece of calico, about 8 inches square, is placed 

 upon the top of the tube E, and a small weight is placed over 

 it to keep it in position. In order to stretch this calico and to 

 keep its surface horizontal, tinned bent wires are passed through 

 its corners and inserted in wooden pegs fixed to the board C D ; 

 the instrument thus adjusted may remain without any further 

 interference until it is found requisite to clean the calico by 

 washing. The calico is thus always kept in a damp condition 

 by absorption ; and as the moisture is being evaporated from its 

 surface, the water in the horizontal tube A B moves towards B 

 with a velocity proportional to the rate of evaporation ; this rate 

 of evaporation, therefore, is indicated by the space passed over 

 by the extremity of the water column in the tube A B in suc- 

 cessive equal intervals of time; and further, as the section of 

 this tube is known, the number of cubic inches of water evapo- 

 rated in any proposed time becomes known. When the liquid 

 has reached the extremity B of the scale, fresh water is added 

 to the tube by the funnel J. The delicacy of the indications of 

 the instrument is such, that at a mean temperature, and at an 

 average state of dryness of the atmosphere, the water in the tube 

 A B will move at the rate of about 2 inches per hour. Having 

 determined the rate of evaporation from the surface of water as 

 compared with that which takes place from the surface of damp 

 calico, the indications of the instrument may be readily reduced 

 so as to give the rate of evaporation from the surface of still 



