130 Daiiiell on a new Hygrometer. 



The balls a and h, together with their connectina; tube, are 

 made of very thin brass. To the orifice/ is soldered a small 

 piece of platinum tube, which, from its property of welding with 

 glass, allows of the junction of a piece of glass tube of the re- 

 quisite length, which, after the instrument has been boiled as 

 before directed, is hermetically closed in the usual way. The 

 thermometer d e is so constructed that its bulb, which is enclosed 

 in the ball b, is rather less than the diameter of its stem, which 

 is made proportionably thick. It is ground air-tight into a 

 collar of brass made for its reception on the top of the ball. The 

 ball a is covered with thin muslin, and the ball b is very highly 

 polished. 



The great advantages of this form of the hygrometer are two. 



First, It enables the observer to mark with the utmost pre- 

 cision the instant of the first precipitation of the vapour. 

 The white mist is directly seen, whereas it requires a little prac- 

 tice to obtain an equal degree of certainty with the glass in- 

 strument, especially in hazy weather. The polish of the metal 

 is easily preserved by means of frequent wiping with leather 

 covered with a little whiting, but the hygrometer would be more 

 elegant as well as less liable to tarnish if strongly gilt. 



The second advantage is that its sensibility may be in- 

 creased at pleasure, by extending the scale of the thermometer 

 d e. The divisions of the thermometer included in the glass 

 instrument are necessarily small, but those of the external ther- 

 mometer may be made of any required magnitude without 

 rendering the bulk of the whole too great. 



I have continued my observations with the new hygrometer 

 for another quarter of a year, as subjoined in the Meteorological 

 Journal, and I shall now endeavour to draw two or three con- 

 clusions from the mean results of the experiments. The means 

 of the half year are as follow : 



Pressure of the atmosphere 29.765 ins. 



do. of the vapour, 0.288 



Weight of vapour in a cubic foot, 3.243 grs. 



Degree of dryness, 3°. 



