Hygrometer 

 Katie, of it. 



205 VERY SENSIBLE HYGROMETER. 



has a beard Accident led me to remark, that the bearded seed of this 



•fmoUture g rass possessed an extreme sensibility of moisture; and 

 being then in want of an hygrometer ', I constructed one 

 of this material, which, on trial, far exceeded my expec- 

 tations. 



ABCD, PI. VI, fig. 1, represents a piece of wood, 

 about fourteen inches long, three inches broad,, and one 

 inch and two tenths thick. The upper part is cut out, 

 as in the figure, to the depth of two inches, leaving the 

 sides A and B, about three tenths of an inch thick. The 

 wood, thus prepared, is morticed into a square board, which 

 serves as its support. 



Fig. 2 is an ivory wheel*, about an inch and two tenths 

 diameter, and two tenths of an inch broad at the rim. A 

 semicircular groove is made in the circumference, of such 

 a depth, that the diameter of the wheel, taken at the bot- 

 tom of the groeve, is one inch. Through the axis, which 

 projects on one side four tenths of an inch, a hole is made, 

 the size of a common sewing needle; and, on this, as a 

 centre, the wheel should be carefully turned ; for, on the 

 truth of the wheel the accuracy and sensibility of the in- 

 strument chiefly depend. From the bottom of the groove 

 a small hole is made obliquely through the side of the 

 wheel, to admit a fine thread. AH the superfluous ivory 

 should be turned away, that the wheel may be as light as 

 possible. 



Fig. 3 represents a piece of brass wire, two inches long; 

 on one end of which a screw is made, an inch and a half in 

 length; and, in the other, a notch is cut, with a fine saw, 

 to the depth of half an inch. This part is tapered oft*, so 

 that the notch, which is intended to hold the beard of grass, 

 in the manner hereafter described, may be closed, by means 

 ©f a small brass ring (a) which slides on the taper part of 

 the wire. 



A little below the centres of the semicircles A and B, 

 fig. 1, two holes are made, precisely in the same direction : 

 one of these is intended to receive the screw, fig. 3, and the 



* Tn my first rtcpdflmenta 1 used a wheel made of card'paper, with aa 

 axis of wood,. which answered very well. 



othtr 



