492 DESCRIPTION OF A NEW HYGROMETER. 



counts of the utility and conveniency of the Sym- 

 piesometer, as are well calculated to recommend it to 

 the attention of those sailing in vessels of the smal- 

 lest burden. It is now in use in the service of the 

 Commissioners of the Northern Lights, on board 

 the Light-house Yacht, of 80 tons register, and the 

 Pharos, or Bell Rock Tender, of 45 tons." 



II. — New Hygrometer. 



In the winter of 1816, I made many trials of dif- 

 ferent substances, for the purpose of ascertaining 

 their hygrometric powers, in order, if possible, to find 

 one which should possess sufficient sensibility, and, 

 at the same time, not to be liable to change the ex- 

 tent of its contraction between the extremes of dry- 

 ness and humidity. Among the various substances 

 which I tried, those that changed their bulk in a 

 considerable degree by a change of humidity, were 

 Rottenstone, Chalk, unbaked Clay made very thin, 

 and Mountain Cork. Though, from the friable na- 

 ture of the three first, it was found difficult to use 

 them, yet I am of opinion, that they may be advan- 

 tageously employed in the construction of hygrome- 



