1^4 Account of a Defcent 



quality of the produft, which in fomc cafes is altered and 

 dccoiTipofed. Tliefe phenomena may be rendered very fen- 

 fible by cooling the upper part of the retort of the fand-balh 

 at the moment when the diftillation is moft aftive: the va- 

 pours fucceflivciv become vjfible in the infide, and drops are 

 condenlc.i on the fides, which loon run down and join the 

 liquor contained in the retort. 



Befides, the contraftion at the upper part of the boiler 

 forms a kind of eoHpile, where the vapours cannot pafs with- 

 out difiicuhy, which neccflarily requires a more confiderable 

 force of afcenfion. This fail has been properly explained by 

 Baumc. 



3d, The capital is not confi;ru6^cd in the moft advantageous 

 manner: the head acquires almoft the temperature of the 

 vapours, whicl), being ftrongly dilated, prefs on the liquid 

 and confine its afcent. 



4th, The niettiod of managing the fire is no Icfs improper 

 than the form of the apparatus: the aft-hole is every where 

 too fmall, the fire-place too large, the door badly Ihut, &c. 

 fo that a current of air is eftablillied at the door, and is pre- 

 cipitated into the chimney, pacing over the coals. Confe- 

 quently, a violent fire is required to heat the boiler mode- 

 rately. The grate is choked up with a thick ftratum of 

 combuftibles, To that they become nearly uleiels for want of 

 a free circulation of the air. 



[ To be continued. ] 



XXT. Account of a Defcent into the Crater of Mount Vefuv'ius 

 hy eight Frenchmen on the jSlight between the ihtb and 

 igih of July 180X. 



X O afccnd to the fummit of mount Vefuvius, which is 

 elevated 3'^co feet above the level of the fea, is an enterprife 

 of great difficulty, as it is necelVary for nearly half the height 

 to climb an exceedingly ileep declivity up to the knees in 

 aflies. Some j)hi!ofophical men of eminencCj however, as 

 Spallanzani, Doloniicu, Dr. Moore, &c. have overcome all 

 thefe difficulties. Sir William Hamilton, who caufed a great 

 many views of Vefuvius to be uciigned during his long refi- 

 dence at Naples, afceuded to the fummit of it fixty-two 

 times; but no cue, at lealt fince the eruption in 1779, ever 

 ventured to dcfccnd into the crater of this volcano, not even 

 Sir William Hamilton, who confidered it Under fo many 

 puints of view, and who vifjtcd it fo tiiany tiuies. It was 



refexved 



' 



