250 



ance of being able to observe a phenomenon of equilibrium instead of 

 one of motion in taking the dew-point. 



Another form of the hygrometer adapted to an observatory, or to 

 occasional observations, consists of a trough, containing mercury, 

 one face of which is of steel, or of gilded copper; the end being con- 

 nected, as before, with a box for containing the materials, to reduce 

 the temperature of the mercury in the trough. A deposit of dew 

 having appeared on the surface of the trough, and having become 

 stationary, so as to indicate that equilibrium is attained, a thermo- 

 meter plunged in the mercury is brought opposite to this point, and 

 indicates the temperature of the surface. 



A very portable instrument of the same kind acting very rapidly, 

 and if deemed advisable by the motion of heat, consists of a cylinder 

 of small diameter, of copper, having a strip of gilding upon one side, 

 and containing mercury. A thermometer, fitting loosely into this 

 cylinder, has a slip of metal projecting downwards from the scale, 

 which terminating opposite to the centre of the bulb, shows the po- 

 sition of the bulb when this latter is immersed in the cylinder. The 

 temperature of the lower end of the cylinder being reduced below the 

 dew-point, a deposit takes place upon the surface ; and by following 

 it as it advances, with the end of the projection from the thermome- 

 ter scale, which gives the position of the bulb, the dew-point is 

 readily ascertained. 



Professor Bache gave further details in relation to these instruments, 

 and compared their qualities with those of other dew-point hygrome- 

 ters, and especially with the instrument of Professor Daniell. He 

 stated, that at a future meeting he hoped to show to the Society the 

 different forms of the instrument in action. 



Mr. George Ord was elected Librarian of the Society for 

 the current year. 



The following standing Committees were appointed for the 

 current year: — 



Of Finance. — Messrs. C. C. Biddle, Patterson, Kuhn. 



Of Publication. — Messrs. Lea, Hays, Fisher. 



On the Hall. — Messrs. Campbell, Richards, G. W. Smith. 



On the Library. — Messrs. Hays, Campbell, Penington. 



The Committee on the trust funds reported upon the subject 

 of the claims of the City Councils, which had been referred to 

 them on the 19th August last, and presented certain resolutions 

 in relation thereto, which were laid on the table. 



