494 DESCRIPTION OF A NEW HYGROMETER. 



and prevented from being injured by any slight ac^ 

 cident ; and the instrument is also less affected by 

 any change of temperature. 



A convenient portable hygrometer may be made, 

 by employing aslip of this membrane, and attaching 

 its extremities to the end of a lever, somewhat like 

 the small pocket metallic thermometers. The ex- 

 ternal appearance of one of these instruments is 

 shewn at the bottom of the Patent Sympiesometer, 

 represented in Plate XXV. Fig. 1. 



Although this membrane is not entirely free from 

 the change to which all animal and vegetable sub- 

 stances are liable, yet hygrometers made of it pos- 

 sess a considerable degree of uniformity amongst 

 themselves ; and, in point of sensibility, this mem- 

 brane exceeds every other substance that I have 

 met with. 



