PROFESSOR OLMSTED'S OBJECTIONS. 431 



that all this great quantity of caloric is radiated off into 

 space as it is evolved, in the formation of cloud? It is a 

 mere hypothesis, without any experiments to support it. 

 Nay, it is contrary to experiment; for if steam is let out of 

 a steam boiler into the air, when it makes cloud, we know 

 it gives out no more caloric to the air than an equal quan- 

 tity of vapor in the atmosphere gives out when it forms 

 cloud; for the sensible and latent caloric of steam, when 

 added together, is a constant quantity, equal to 1242 Fahr., 

 as appears by the beautiful experiments of Professor W. R. 

 Johnson, of Philadelphia. At least, he has proved that the 

 latent caloric of steam, at the temperature of 212, is about 

 1030 ; and it is generally admitted that the latent caloric of 

 steam diminishes as the sensible increases. 



But all this doctrine aside, it is proved by experiments with 

 the nephelescope, that only about one half as many degrees 

 of cold are produced by a given expansion when cloud is 

 formed, as when air so dry is used that no cloud is formed. 

 This experiment was not even mentioned by the Professor, 

 though it was brought forward prominently by me as proof 

 positive and undeniable, of the entire truth of my theory, 

 and that, too, independent of all knowledge of the phys- 

 ical laws of latent caloric, and the specific caloric of air. 



Before my theory is proved false, that experiment must 

 be refuted. But the Professor exultingly said, that "the 

 experiment which I adduced to prove that cloud is warmer 

 than surrounding air, proved his doctrine of radiation, 

 namely, the etheriscope of Leslie ; when that instrument 

 was turned towards a cloud the thermometer rose, and 

 when turned away from the cloud, towards the clear sky, 

 the thermometer fell." 



I will not argue this point; the whole scientific world 

 will agree with me that the thermometer rose in conse- 

 quence of the superior heat of the cloud. It is true the ex- 

 periment proved that the cloud radiated ; but it proved like- 



