214 On the Cold Caves of the Monte Testaccio at Rome. 



change of wind. For were the wind to wheel from the N. E. 

 to S. W., I have very httle doubt that next day the tempera- 

 ture of the cellars would be found to have increased. If o com- 

 paratively moderate a heat as 78° at Rome, in the middle of 

 summer, may well be supposed to arise from the " Tramon- 

 tana,'" after crossing the extent of the Campagna, which in 

 winter blows such a dry chilling blast. We have already ob- 

 served (p. 206) that in February 1827, Saussure's hygrometer 

 stood at 52°, or in the ratio to saturation of .294-. From my 

 own Meteorological Journal, I find that in 13 days out of the 

 28, the wind was from the northern points, and on nine more 

 it was variable ; whereas in the 31 days of January it blew only 

 eight days from those points, which may be considered a suf- 

 ficient illustration of the fact. I have only farther to add on 

 this point, that there is another and most legitimate source of 

 coolness we have not yet noticed. Lumsden's observations 

 sufficiently prove that a current of external air enters by the 

 top of the door of the cellars ; is cooled as it proceeds inwards ; 

 joins the cool air of the mountains ; and comes out by the bot- 

 tom of the door.* Now nothing can be more evident than 

 that, as the interior of the caves are saturated with moisture in the 

 coolest state, which all the circumstances we have before con- 

 sidered could reduce it to, that is, from 45° to 50% a new 

 quantity of dry external air comes upon it in that state, and 

 must experience a great reduction by being moistened with 

 such cool humidity. It is this new air which fills the caves, 

 and which creates the currents. It is necessarily it which has 

 its temperature taken ; and it must necessarily be coolest at the 

 bottom of the back of the cellar, as Lumsden found it, (see 

 pao-e 206.) This gives the concluding touch to the reduction of 

 temperature, and is, I have no doubt, sufficient to produce 

 even that cold which Saussure observed ; and all the other 

 cases on record will be easily solved by it. 



In concluding these remarks, which have swelled so much 

 beyond my original intention, I may be allowed to remark, 

 that if it is thought by any that I have not made good the 

 point I have proposed ; that the certain determination is only 

 what extensive experiments on the spot can give ; and that I 

 • See his work, pp. 172 and 173. 



