On the Cold Caves of the Monte Testaccio at Rome. 21S 



imbued with moisture, the air of the atmosphere being sup- 

 posed at the dryness to saturation of .238, is instantly reduced 

 to a state of saturation ; and, in the^r6'^ place, to a temperature 

 of 54°, (by formula ;) but also to a point several degrees lower, 

 because the moisture contained in the pottery had a tempera- 

 ture of 60° instead of 78°. As the current forces itself inwards, 

 and constantly reduces to 53° or 54° the tiles and fragmerits 

 in the interior, which by and by assume the same temperature, 

 and about the middle of summer may produce fresh evapo- 

 rative force, as the heat of the sun may have prevented the 

 full acquisition of humidity in passing through the outer 

 stratum ; and as we approach the centre of the mountain, 

 these causes will always increase in rendering the moistening 

 agent of a lower and lower temperature. It is the vast bulk 

 of the hill which must necessarily produce more powerful and 

 extended effects than our petty experiments and minute rea- 

 sonings can enable us to judge of; and in some extreme cases 

 may produce a cold of 44 or 45. Saussure, in his account of 

 the Monte Testaccio, has treated the subject not very philo- 

 sophically, particularly when he considers the evaporative force 

 the same at all seasons, which arises from the obscurity of hy- 

 grometric science at that period ; and I think it may be ques- 

 tioned how far even its present state can admit such extended 

 inathematical formulae as are now applied, and which I have 

 so much employed in this paper. Be it ever remembered, that 

 these Jbrrmdoe are founded merely on experiments on a small 

 scale, which must ever give more partial and incomplete re- 

 sults, (though they may agree well with one another when 

 made under similar circumstances) than in the vast operations of 

 the example before us. Saussure, however, states one impor- 

 tant fact, that he considers the observations of the Abbe Nollet 

 in 1739, and therefore by analogy those of Lumsden in 1762, 

 as strictly comparable with his own. The former found the 

 temperature, Sept. 9th, when th^ air was 72|°, to be 53|°; and 

 the latter, Aug. 26th, with the air at 79°, to be 54J°. To ac- 

 count for this rise of temperature at the end of summer, he has 

 an unsatisfactory theory of capacious, cool, and dry caverns ; 

 but we are able to account for it in an instant, either generally 

 by the setting in of damp weather, or particularly by a simple 



