On the Cold Caves of the Monte Testaccio at Rome. 211 



gularly at intervals upon the thermometer. The temperature 

 of the room was 64% and a moistened thermometer fell to 57°» 

 The grains in cubic inch were .0025635, on the degree of dry- 

 ness .668. The heated air was at first 81°; and, after a con- 

 siderable time, had fallen only two degrees. The thermome- 

 ter became stationary at 59°. By making the proper propor- 

 tions, I find that the dryness of the heated stream of air in 

 these three experiments, using the mean temperature of 77% 

 8I|°, and 80% was respectively .482, .347, and .411. 



Now, the results of these experiments go to prove, l^^, the 

 circumstance which I have already insisted on, the small im- 

 portance of the state of the air within the mountain, or at 60°. 

 Although the temperature of the room varied from 59 J to 64, 

 the final results are all within the limits of 59 and 60, because 

 the condition of the surrounding air is always that of satura- 

 tion; and a difference of 5° in the temperature of the humidity 

 applied, (which is the most important agent,) gives no sensible 

 alteration. The differences of result are solely owing to the 

 change in condition of the hot stream of air applied. They can- 

 not be ascribed to the different forms of the experiments ; for 

 it is sufficiently evident, that, whether the thermometer be 

 simply applied to the direct blast of air heated to the high de- 

 gree of 80% and the reduction of temperature left to the simple 

 coating of the moistened bulb ; or whether the air reach the 

 moistened bulb in a state of saturation, and surrounded by 

 pots, which contribute to cool an atmosphere round it, as in 

 the first experiment ; or as in the second, whether the air 

 reaches it already cooled down to the circumambient tempera- 

 ture, and loaded with moisture, the difference of result is 

 wholly unimportant. In the second place, these experiments 

 prove the influence of having the humidity which moistens the 

 surfaces, over which the hot air passes, of a temperature con- 

 siderably lower than that of the air itself, which is the sole 

 effect which I am disposed to attribute to the comparatively low 

 temperature, (that of 60°,) which undoubtedly exists within the 

 mountain. For let us take the case of the third experiment, 

 and find what coolness would have been produced by air of 80° 

 impinging on a surface moistened with water at its own tempe- 

 rature; or rather in this case, what dryness was required in the 



