VERY SENSIBLE HYGROMETER. QQg 



ather a gold pin, which is to project four tenths of an inch 

 beyond the inside of the part A. The pin is made rather 

 smaller than the hole in the axis of the ivory wheel, and is 

 highly polished ; in order that the motion of the wheel may 

 be the' less impeded by friction. 



Two fine threads, about fourteen inches long, are passed 

 together through the hole in the groove of the wheel, and 

 are prevented from returning, by a knot on the outside. 

 To the ends of these threads two weights are attached, ex- 

 actly similar, and just heavy euough to keep the threads 

 expended. 



One of the threads having been wound on its circumfe- 

 rence, the wheel is to be placed on the pin, about the tenth 

 of an inch from the side A, as in fig. 4. Two glass tubes, T 



of a sufficient bore. to admit the free motion of the weights, 

 are fixed in grooves, in such a manner, that each thread 

 should fall exactly in the axis of the tube. The tubes are 

 so long as nearly to touch the ivory wheel. 



The beard of the obbeena hooloo, being prepared by cut- 

 ting off that part which is useless, is inserted about the 

 tenth of an inch in the projecting end of the axis of- the 

 wheel, and confined by a small wooden pin, which is to be 

 tyroken off close to the axis ; the other end is placed in the 

 notch of the brass screw, before described, and secured by »<ir A 



means of the sliding ring. «" >d \H§r 



It is evident, that when the grass untwists, the wheel will Action of.the 

 turn on the gold pin ; and the thread, which is wound about ^^ xomc er * 

 it, with the weight attached, will desceud in the one glass 

 tube ; while, on the contrary, the weight on the opposite 

 tube will ascend, and vice versa. 



The beard of the grass is now to be thoroughly wetted, Adjustment * 

 with a hair pencil and water; and when the wheel is sta- • m0isture 

 tionary, the weights are to be so adjusted, by turning the 

 brass screw, that the one shall be at the top, and the other 

 at the bottom of the glass tubes ; which points will mark 

 extreme moisture. 



The instrument must then be exposed to the sun, or to and dryntM. 

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

 to obtain a considerable degree of dryness. The weights will 

 now hange situati ; and, ,probably, on the first trial. 



Vol. XXIII.— July, 1800. P - wiU 



