A VERY SENSIBLE HYGROMETER. 55 



A seed being chosen, the top of it was cut off, it 

 liaviPig been found by experiment to be perfectly in-^ 

 sensible. A straw, the lightest that could be procured, 

 two inches and a half in length, and coloured at the 

 end intended to be the index, wsls divided longitudi- 

 nally, in the middle, by the point of a fine pen-knife: 

 the knife was then turned a little on one side, till the 

 opening was wide enough toadmit the beard of 

 grass; which being inserted, and the point of the 

 knife withdrawn, the straw closed and held the beard 

 of grass sufficiently firm. 



Not being able to procure workmen, capable of 

 executing what I wished ; tlie hygrometer, thus pre- 

 pared, was fixed, in a rude manner, to the circular 

 plate at the bottom of the box, by means of a piece 

 of sealing wax, in which a very small hole had been 

 made, with a hot wire. The beard of grass beino- 

 placed in the hole, it was closed, by touching the wax 

 on one side with a heated wire, taking care to set the 

 grass as upright as possible. 



Tt remained now to determine the extremes of 

 dryness and moisture, and to fix on som.e mode of 

 division, by means of which this hygrometer mi^'lit 

 be comj)ared with any other. 



A new earthen pot was made very hot, by put- 

 ting fire within, as well as around it; and when it 

 was supposed to have been sufficiently burnt, to be 

 perfectly free from moisture, the fire was taken from 

 the inside, and the pot suffered to cool, till the air in 

 it was of the temperature of l60°, but not lower. The 

 hygrometer was then placed in the pot, being kept 

 from touching the bottom, by means of apiece of drv 

 wood ; and it remained there nearly an hour ; lono- 

 before the expiration of wdiich time, the index was 

 perfectly steady. The hygrometer was then quickly 

 taken put of the pot, and the circular plate, carrying 



