On the Cold Caves of' the Monte Teataccio at Rome. 207 



lead to mistakes in recording the indication of the instrument/' 

 In this case, therefore, 55° indicates on the common scale ^S* 

 from dryness, and 48°, 52°. Now, 45'' of Saussure is equiva- 

 lent to .^413 parts of saturation, (see the above quoted arti- 

 cle,) a degree of dryness very much greater than .346, which 

 it was thought could not be counted upon. 3J, The influence 

 of the localities, as well as of the latitude, in altering the hy- 

 grometric state of the atmosphere, does not seem to have been 

 sufficiently considered. The writer of the article before us 

 elsewhere observes, * that " the quantity of moisture mechani- 

 cally con^bined with the air over different regions, must de- 

 pend, in the Jirst place, on the mean temperature ; and, se-. 

 condly, on the presence of a sufficient quantity of water at the 

 surface of the earth, to afford an adequate supply of moisture 

 to the atmosphere by evaporation." And though he observes 

 that such dryness as .346 can seldom occur but in northern 

 latitudes, he elsewhere remarks, -f that the distressing effects 

 of the Sirocco and Simoon arise from the power oi iheix extra^ 

 ordinary dryness on the human frame. That this does not hold 

 with regard to the Sirocco in Italy, my remarks, No. xiv. 

 p. 263, sufficiently prove, which is evidently owing to the 

 crossing of so large a portion of the Mediterranean. But an 

 extremely dry cold wind comes from the northern quarters 

 called the " Tramontana," which prevails in winter, and with- 

 out doubt lowered the hygrometer in February to such a de- 

 gree as was stated above. Besides, if we consider the situation 

 of Rome, we shall not be surprised that in summer the wind 

 should be excessively dry. Sterile arid deserts surround it on 

 every side from twelve to at least eighteen miles distance ; and 

 towards the north particularly, whence the dry winds un- 

 doubtedly blow, the plains are extremely extensive, flat, and 

 barren ; abounding in every direction with small volcanic rising 

 grounds, composed of ashes, breccia, tufa, and pozzulana, than 

 which few substances show more avidity for moisture. Shall 

 we then wonder that Rome frequently labours under excessive 

 brought ? The copious streams of delightful water which sup- 

 ply fountains in every street and square of the eternal city 



* Edinburgh Encydopcedia, Art. Physical Geography, p. 508. 

 + Ubi supra, p. 505. 



