A VERY SENSIBLE HYGROMETtR. fff 



will descend in the one glass tube; whilst, on the con- 

 trary, the weight on the opposite tube will ascend, 



and I- ice versa. 



The beard of the grass is now to be thoroughly 

 wetted, with a hair pencil and water, and when the 

 wheel is stationary, the weights are to be so adjusted, 

 by turning the brass screw, that tiie one shall be at 

 the top, iand the other at the bottom of the glass 

 tubes, which points will mark e.vti'eme moisture. 



• 



The instrument must then be exposed to the sun, 

 or to some heat, not powerful enough to injure it, but 

 sufficient to obtain a considerable degree of dryness. 

 The weights will now change situations; and, pro- 

 bably, on the first trial, will continue to move beyond 

 the glass tubes. Should this happen, ib.e beard of 

 grass is to be shortened, by sliding back the ring, 

 and advancing the brass screw, so as to include a 

 longer portion in the notch. Other trials are to be 

 made, and the length of the grass varied, till th.e ex- 

 tremes of dryness and moisture are within the limits 

 of the glass tubes. 



As this instrument cannot conveniently be exposed 

 to so high a temperature, as is necessary to obtain ex- 

 treme dryness ; this point may be ascertained bv 

 ■mediVis oi' 2i standard circular Jiygrometer. The point 

 of extreme moisture has been already determined; 

 and in the circular hygrometer^ the number of revolu- 

 tions, &c. between the extremes is known. The two 

 hygrometers are to remain sometime togetlier, that 

 they may be in the same state wirli respect to mois- 

 ture; marks are then made, where the v/ciglits rest 

 in the glass tubes, and the degrees shewn by the in- 

 dex of the standard hygrometer noted- Lastly, llie 

 distance between these marks and extreme moisture, 

 is to be divided into the same number of equal parts, 

 as are indicated by the standard hygrometer, and the 



