the Dew-point by the Wet-bulb Hygrometer. 471 



tions be calculated, and, from a comparison of it with the ori- 

 ginal temperature of the air when saturated with humidity, 

 we shall be enabled to pronounce with confidence upon the 

 value of our method. 



In the experiments which I performed on this plan, the air 

 was saturated with moisture by forcing it from a bellows 

 through a succession of four Woulfe's bottles, connected in the 

 usual way, so as to cause the air to pass in each bottle through 

 about two inches of water, and the air thus saturated was 

 heated by being made to pass through a coil of copper tubing 

 immersed in a tub of warm water, the thermometer and hy- 

 grometer being placed with their bulbs within a quarter of an 

 inch of each other in a narrow glass tube attached to the 

 further extremity of the copper worm. The following are the 

 results thus obtained : 



By a glance at the preceding table, which includes twenty- 

 four distinct observations, we shall perceive, 1st, That in the 

 case of seven of them the observed and calculated dew-points 

 are almost coincident ; 2nd, That the difference in no instance 

 exceeds, and in but a single instance reaches, one degree ; and 

 3rd, That the mean difference deducible from the whole is 



