£]0 VERT SENSIBLE HYGROMETER. 



will continue to move beyond the glass tubes. Should this 

 happen, the beard of grass is to be shortened, by sliding 

 back the ring, and advancing the brass screw, so as to in* 

 cTude a longer portiou in the notch. Other trials are to be 

 made, and the length of the grass varied, till the extremes 

 of dryness and moisture are within the limits of the glass 

 tubes. 

 V onvemV.ca jf the whole of that part of the oobeeva hooloo, which 

 of tkistorm. possesses the hygroscopic property, be used, the scale will 

 comprise more than twenty-four inches; a length, which, 

 though perhaps useful on particular occasions, will not be 

 found convenient for general purposes. 

 Trial of itsae- From an idea, that in a high state of moisture the grass 

 curacy. would not retain sufficient power to move the wheel equa- 



bly, it was thoroughly wetted, till it indicated extreme 

 moisture, and, while in this state, the wheel was drawn 

 round, by laying hold of one of the threads: on releasing 

 it, it instantly regained its former situation, with consider- 

 able force. The same experiment was made, in various 

 Other states of moisture, and it was always found, that the 

 weights returned immediately to the degree from which they 

 had been removed. 



t metal wheel J fc wou ^4 perhaps be an improvement, if a light wheel 

 iy be used, of brass, or any other metal, not liable to rust, were use4 

 instead of the ivory one; the grass having been found, by 

 experiment, to be capable of moving a wheel pf lead. The 

 axis of the wheel might be made very small, and supported 

 pn Ys, which probably would add much to the sensibility 

 of the instrument. 

 Adapted to J nave vet nac * no opportunity of comparing this with any 



slight variation other hygrometer ; but it is simple in its construction, not 

 o$ moisture. ^ as j]y disordered, and should seem, from the extent of its 

 scale, to be particularly adapted to experiments, in which 

 small variations of moisture are to be observed. 

 H rrometrl al The hygrometer has been hitherto an instrument rather of 

 observations curiosity than utility. But from most accounts that we 

 Skmfau have, *w appears very probable, that this instrument has 

 more to do with the phenomena of refraction* than either 

 barometer or thermometer. If then we could obtain a 

 ji umber of observations of apparent altitudes together 



with 



