34 PHILOSOPHY OF STORMS. 



In short,' I performed experiments with the instrument thus 

 modified, both on dry air in which no cloud could be form- 

 ed, arid in air saturated with vapor, in which a dense cloud 

 was formed, and the results for small expansions, do not 

 vary materially from those given above. The instrument, 

 thus modified, I have named a nephelescope, or cloud- 

 examiner. 



It was soon discovered, however, on using high degrees 

 of condensation, that the ratio of cold produced by the ex- 

 pansion of air from diminished pressure, was a decreasing 

 one, as the quantity of air pumped into the nephelescope 

 was increased. 



What the exact ratio of this decrease is, I am not pre- 

 pared to say ; probably as the square root of the density of 

 the air previous to expansion. It is very desirable to know 

 this law; and perhaps, by a careful set of experiments, 

 performed with the nephelescope on dry air, it may be 

 discovered. 



I have given below a few experiments at different densi- 

 ties. The measures are all in quarter inches and tenths of 

 quarters. 



