39*5 DESCRIPTION OP AN IMPROVED HYGROMETER^ 



The extremes of dryness and moisture are determined 

 in the following manner. The Hygrometer is placed 

 in a new earthen pot, which has never been wetted, and 

 exposed for a considerable time to as great a heat as 

 the grass can bear without injury : when the index is 

 perfectly steady, the Hygrometer is to be taken out of 

 the vessel, and the screw at c, turned round with a pair 

 of pincers, so as to bring the gold loop to xht first inter - 

 vai of the screw on the axis, counting as before from 

 the dial plate, (which is to be placed to the left hand) 

 and the index to 100 or zero. The Hygrometer must 

 now be suffered to cool gradually, during whicli, if the 

 atmosphere be in a mean state of moisture, the index 

 will make four or five revolutions ; the oobeena hooloo 

 is then to be continually wetted with a hair pencil and 

 water, till the index is again perfectly steady. This 

 will require some time, as it moves very slowly when 

 within a few degrees of extreme moisture. The degree 

 at wliich the index stands is now to be noted, and the 

 number oi intervals counted between the dial plate and 

 o^old loop, and this number prefixed to the observed 

 deo-rees will give the extent of the scale. 



All observations made with this Hygrometer, are to 

 be reduced to what they would have been had the scale 

 consisted of 1000 parts, or ten revolutions of the index. 

 This is most convenient, as itfacihtates the comparison 

 of observations made with different Hygrometers. An 

 example may not be thought superfluous. Suppose 

 the scale of the Hygrometer to be 1 145, or eleven in- 

 tervals and forty-five parts ; and that at the time of ob- 

 servation, there zrtfoiir intervals, between the dial plate 

 and gold loop, and 50 farts shown by the index; this 

 would be written 450. Then, as {\45 : 1000 : : 

 450 : 3(j3 nearly, the number of degrees to be regis- 

 tered. 



