Vropofalfor a rietu Hygrometer. 37* 



5. Apply the glafs-plate thus moiftened again to the ba- 

 lance, and bring the latter into equilibrium by fcrewing the 

 leaden bullet. Mark then the place at which the bullet 

 ftands, as the higheft degree of moifture. 



6. This apparatus is to be fufpended in a fmall box of 

 well-dried wood*, fufficiently large to fuffer the glafs-plate to 

 move up and down. An opening muft be made in the lid, 

 exactly of fuch a fize as to allow the tongue of the balance to 

 move freely. Parallel to the tongue apply a graduated circle, 

 divided into a number of degrees at pleafure from the higheft 

 point of drynefs to the higheft degree of moifture. The box 

 muft be pierced with fmall holes on all the four fides, to give 

 a free paifage to the air ; and to prevent moifture from pene- 

 trating into the wood by rain, when it maybe requilite to ex- 

 pofe it at a window, it muft either be lackered or painted. 

 To fave it at all times from rain, it may be covered, however, 

 with a fort of roof fitted to it in the moft convenient manner. 

 But all thefe external appendages may be improved or al- 

 tered as may be found neceffary. 



VII. Method employed in Spain for making the Alcarrazas, 

 or Veffels ufed therefor cooling Water. By Cit. LaSTEYRIE. 

 From the Journal des Mines, No. XXXIV. 1798. 



x\LCARRAZAS are a kind of veflels ufed in Spain for 1 

 cooling water intended for drinking. As they are exceed- 

 ingly porous, the water oozes through them on all fides ; 

 the air which comes in contact with it, by making it evapo- 

 rate, carries ofF the caloric contained in the water in the 

 Veflel, and by thefe means renders it remarkably cool \. 



Thefe 



* We would recommend a glafs cafe. Edit. 



t It is a principle, univerfally admitted, that a liquid, palling to a 



ftate of vapour, appropriates to itfelf a quantity of caloric, which it takes 



from thofe bodies with which it is in contact. The more volatile a liquid 



is, the more rapid will be this effect ; and it is on this principle that che- 



B b a milts, 



