On the Cold Caves of the Monte Testaccio at Rome. 205 



Art. III.— 0/i the Cold Caves of the Monte Testaccio at 

 Rome, By a Coreespondent. 



Happening recently to notice in the tenth volume of the 

 Edinburgh Philosophical Journal^ some remarks on the causes 

 of the remarkable coldness of the cellars in the Monte Testac- 

 cio at Rome, I was surprised to observe that the ingenious 

 author of that paper denies the influence of evaporation in pro- 

 ducing that cold, — an explanation which I have always under- 

 stood to be deemed so generally satisfactory, that, during a late 

 residence in Rome, I did not think of investigating minutely 

 this remarkable phenomenon, which neglect I now extremely 

 regret. 



Some mistakes in the data and misconceptions of the locali- 

 ties shown by your correspondent, induce me to offer some im- 

 perfect remarks towards defending the theory of evaporation, 

 and to lay before that gentleman a few hints for the correction 

 of his observations, to which no one will be more able to apply 

 the rigid mathematical investigations which he has elsewhere 

 so successfully employed. Indeed, the science of hygrometry 

 has lately received such an accession of accuracy, and such ex- 

 tension of limits, that I found my inquiries more difficult and 

 minute than I at first anticipated ; and I shall state my obser- 

 vations with greater brevity than I at first proposed, as I am 

 not so familiar as I could wish with the modern refinements of 

 this branch of meteorology. 



Saussure found the temperature of one of the cellars, July 

 1, 1773, to be 441**, and of another 44°, while the external air 

 was at 78°.l. Now, (says the author of the article in ques- 

 tion,) as a cubic inch of air at 78° can contain .005878 of a 

 grain of water in solution, and at 44° only .00203S, the degree 

 of dryness in the external air must have been ffff, or .346, 

 (saturation being — unity,) = 23° Deluc's hygrometer ; " a 

 degree of dryness," he adds, " which is seldom observed except 

 in high latitudes ;" and a little before remarks, that a state of 

 perfect dryness can rarely occur at Rome. On this I have to 

 observe, l^f. That the present is a very extreme case ; and we 

 may assume the atmosphere to have been in a state which 



VOL. VIII. NO. II. APRIL 1828. o 



