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



" seldom'" and " rarely'** occurs at Rome. That this was so, 

 the following observations, taken from *' LumsderCs Antiqui- 

 ties of Rome,'*'' which afford an uncommonly parallel instance, 

 will easily show : 



August 26, 1762. 



On the ground at the entrance of the cellar, 

 Four feet from the ground. 

 Top of the cellar, _ - - 



Half way from the door to the farther extremity, 



seven feet from the ground. 

 On the ground, - - _ 



Farthest extremity seven feet high. 

 On the ground, - . _ 



External air in the shade, - . - 



The reputation of Saussure prevents us from a moment 

 doubting his accuracy ; but the external temperature being al- 

 most exactly the same, and the internal so much higher, proves 

 that his was an extreme case. But, 2^, .346 is given as the 

 required degree of dryness, (though we shall presently see that 

 the author has not stated his argument in the strongest light,) 

 and I by mere accident have the means of proving, that a 

 much greater dryness does sometimes occur at Rome. Whilst 

 examining the meteorological diary kept at the Collegia Ro- 

 mano, for the purpose of comparison, shown in my paper on 

 the Horary Oscillations of the Barometer, I kept a note of se- 

 veral of the maximum and minimum results. For 1826, I 

 found the maximum of the hygrometer, August 8th, 55°, and 

 minimum, November 5th, 0*^. For February 1827, the range 

 0® — 48®. The head of the column for the hygrometer is en- 

 titled, " Igro. a Cap.," which, without the possibility of doubt, 

 means " Igrometro a Capello,""* or Saussure's Hair Hygrome- 

 ter. It is, however, evident, that the 0** or zero indicated per- 

 fect dampness, not dryness., as is usual ; but that this is some- 

 times done with common hygrometers, we have the testimony 

 of ihe author himself, * after mentioning the common arrange- 

 ment. " Some artists, however, reverse this order, and place 

 the zero at extreme moisture, — a practice which cannot fail to 

 * Edinburgh Encyclopasdia, Art. Hygrometry. 



