Tkary of did Sahterratieoiis Winds. 233 



The mountain which overlooks thefe caves is calcareous, its deep fide lying to the north, 

 againft which the huts are placed. Its name is Renq, and its foot advances into the lake 

 of Lucerne, where it forms a promontory. I: is one of the bafes of Mount Pilite, of which 

 it forms part. M. Pcyffer informed M. De SaulTure, that the lake is very deep near the rock. 



It appears that the cold wind ifiues at many places ; for at the foot of the mountain in 

 the neighbourhood, if the earth be any where removed which covers the rubbifli, the cold 

 wind which iffues forth may be felt againit the hand *. 



The tjieory by which M. De Sauffure explains the cold of thefe caves is as follows: 



It mud be fuppofed that the air which cools thefe caves was included in fubter- 

 raneous Cavities, not fufTiciently deep to be inaccelFible to the heat of fummer, and the 

 cold of winter, but yet enough fo to lidmit of a variation of a few degrees from thefe 

 changes. It mufl; alfo be fuppofed, that after tliis air has been fomewhat condenfed by the 

 winter's cold, and the fummer's heat begins to caule it to iflue forth by dilatation, it is 

 pgain cooled by evaporation during its pafiiige through humid clefts, or the intcrftices of 

 wet ftones. 



He thinks that the exiftence of fuch refervoirs, acceffible to the cold of winter and the 

 heat of fummer, is not hypothetical, but an immediate confequence of the fafts univerfally 

 attefted by the pofleflbrs of tliefe caves, namely, that the air ilTues out in the fummer with 

 fo much the more force as the weather is hotter, and returns again by the fame apertures 

 in proportion to the intenfity of the cold. 



Though the cooling efFe£l of evaporation admits of no doubt, he thought it proper to 

 make an experiment refembling what he conceives to happen in this phenomenon. He 

 took a tube of glafs of one inch in diameter, which he filled with fragments of wetted ftone. 

 Through this tube he forced the blaft of a large pair of bellows : the air ilTued out of the 

 bellows at the temperature of 18 degrees, and its paflage through the tube caufed it to de- 

 fcend to 15. He had the fame refult when he ufed a chemical receiver with two necks, 

 half filled with fmall flints wetted ; but when he direded the wind of the fame bellows 

 againft. the ball of a thermometer furrounded with a wet cloth, the refrigeiation was four 

 degrees. A flill greater refrigeration, namely, of nine degrees, was produced by inclofing 

 the ball of the thermometer in a wet fponge, and M'hirling it round in the air. But, as 

 this candid obfervcr juflly remarks, the air in this laft cafe is continually renewed ; fo that 

 the circumftances are not accurately parallel to thofe in which the air is fuppofed to be- 

 come continually more and more loaded with moifture. ' 



* To thefe inOiinces may be added the caves of Roquefort, of which a dcfcription is given by Chaptal in tlie 

 Annalcs de Chimic, IV. 31, 45. From the defciiplion of the caves tbcmfclvts, vvhicli is lefs iTccife tlian thofe 

 cf M. De SaulTure, it appears that the air iffucs from among the fiagnicnts of a calcareous mountain, Thefe 

 caves arc ufed in the manufaifture of a peculiar and liighly eftcemcd chcefe. M. Murcorelle in the month of 

 Oftobcr found the thermometer of Reaumur defccnd in thefe caves to ^i degrees ; while it flood at 13 degrees in 

 the open air; and Chaptal on the 21ft Augnrt I7S7, whh a good tlicrmometcr, which flood at J3 in the (hade in 

 thi open air, found the temperature of a rapid current in one of the caves to be 4 degrees. He was informed 

 thit the ihermometer had been fecn in that cxpofition as low as i degrees above tero. The hotter the external 

 til , ilie cooler tho caves arc fuuiid to be, bccaufc the current is then lironger, 



Mr. Cliaptal fuppofcs, in hit explanation, v;hich is very concifc, ihut the external air enters ilic earth, 

 «nd ii conlcd by cvapor.iiion j but he does not point out any cauft why tlie cuircnt is piuductd, and varies 

 in its velocity in proportion to ihe extcruiil heat. N. 



Vol. I.— August 1797. Hh He 



