459 



quite plain. The brooches or fibulae are composed of an alloy of 

 silver. One of them is of remarkable size, being thirteen and a half 

 inches in length, and six inches in breadth. The front is gilt, and 

 covered with various interlaced patterns, and is one of the finest 

 examples of its class remaining in Ireland. 



L. — On a Modification of Eeonattlt's Condensing Hygeometee, 



WITH ODSEEVATIONS ON THE Ps YCHEOMETEE. By M. DONOVAN, 



M. E. I. A., Member of the Philadelphia College of Pharmacy. 

 [Read April 12, 1869.] 



The dulness produced on the outside of a glass vessel by pouring 

 water into it much colder than itself has given origin to a number of 

 instruments intended to present that result with facility and precision, 

 as a means of ascertaining the quantity of aqueous vapour contained, 

 at any particular moment, in a certain volume of air — of determining 

 the temperature at which it would begin to precipitate, and of disco- 

 vering what quantity of water the atmosphere could still hold in 

 addition to that which it already contains. 



Amongst these, Daniell's Hygrometer held a conspicuous place : it 

 was, however, far from being a satisfactory instrument. Its imperfec- 

 tions have been fully stated by Eegnault. ("Annales de Chimie," xv., 

 p. 194). 



Observing these imperfections, M. Eegnault contrived a Hygrome- 

 ter on the principle of condensation, which he found to act satisfacto- 

 rily. The following is his account of it : — An exceedingly thin and 

 highly polished hollow silver cylinder, the diameter of which is 0*787 

 inch, and its length 1*77 inch, is accurately fitted, by grinding, to a 

 glass tube, open at both ends. The upper end of this tube is closed 

 with a cork, which is traversed through its axis by the stem of a very 

 sensible and correct Thermometer. The bulb, or rather the cylindrical 

 reservoir, of the Thermometer occupies the axis of the silver cylinder, 

 or thimble as Eegnault calls it. A very slender air tube of glass, open 

 at both ends, passes through another hole in the same cork, and 

 descends nearly to the bottom of the thimble. The upper part of the 

 containing glass tube has a small lateral tubulature, which communi- 

 cates, by a slender leaden tube, with a distant aspirator filled with 

 water. When the instrument is to be used, ether is poured into 

 the thimble until it rise a little way above the bulb of the Thermome- 

 ter. The water of the aspirator is then allowed to flow : air passes 

 through the air tube, and issues out of its lower end through the ether, 

 which is thus vaporized, and produces cold. This cooling process is 

 to be cautiously continued until the temperature be found at which a 

 faint cloudiness can be maintained on the silver thimble by the con- 

 densation of atmospheric moisture. 



