Daniell on a neto Hygrometer. 319 



all the vital functions. In bodies debilitated by disease, indeed, 

 the contrary effects may be produced. They may be unable 

 from weakness, to support the drain of free exhalation, which 

 is exhilarating to the healthy ; and hence, probably, arises the 

 benefit of mild climates and warm sea breezes, in cases of con- 

 sumption and diseases of the lungs. Observations of the hy- 

 grometer in places which have been found of service in those 

 complaints, will, not improbably, throw some light upon their 

 treatment ; and may, perhaps, teach us to construct an arti- 

 ficial atmosphere of greater efficacy than any that has yet been 

 recommended on occasions when the relief of local change may 

 be impossible. Observations also in marshy and fenny situa- 

 tions may not unreasonably be expected to explain the diseases 

 prevalent in such districts, and an extension of the use of the 

 instrument to different countries, cannot fail to elucidate many, 

 as yet obscure, peculiarities of situation and climate. 



I shall now proceed to describe the manner of applying the 

 hygrometer to artificial atmospheres, and to detail some expe- 

 riments with it, detached from the preceding series. Plate 5. 

 Fig. 2, represents a bell-glass, prepared for this purpose. A 

 hole is drilled in its side, through which the tube, proceeding 

 from the ball placed under it, containing the thermometer, is 

 passed, and welded with the tube proceeding from the other 

 ball on its exterior side, by means of a lamp ; the stem is 

 then secured in the side of the glass by means of a cement, and 

 the ether boiled, and the capillary opening secured as before di- 

 rected. The exterior ball is then to be covered with muslin. 

 In this way the evaporation from the latter produces a cor- 

 responding degree of cold upon the ball under the bell-glass, 

 and will measure the quantity of vapour included, by the pre- 

 cipitation which may readily be marked. The bell-glass may 

 be secured by grinding, and other well known means, from any 

 communication with the exterior air. 



The hygrometric properties of any substance may thus be 

 easily measured, by placing it under the receiver, and marking 

 the absorption of the vapour. 



Exp. 1. With the thermometer at 60°, 1 found the point of 



Y2 



