1847.] Association of Geologists and Jfaturalists. 211 



itudes, a similar examination was made, to see if the ice had torn 

 off any of the copper, the bottom could not be seen at all. 



Prof. Henry mentioned the commencement of a series of ex- 

 periments on the effects of increased pressure on animals; allud- 

 ing to experiments made by subjecting the common mosquito to 

 great pressure under water. 



Prof. Agassiz remarked that fishes would also live a long time 

 under greatly diminished pressure, if it was gradually effected. 

 He praised very highly the plates of the works of the Exploring 

 Expedition. The plates of fishes were by far the most beautiful 

 he had ever seen, and were an honor to all concerned in their 

 production. The work by Prof. Dana, on corals, &c., would long 

 be the standard work on the subject. 



Prof. Silliman observed that it was much to be deplored that a 

 work of such value as the results of the Exploring Expedition, 

 should be issued in so small an edition, that all would be consum- 

 ed in the gifts which the government would very properly make 

 to other governments and the states. Its result would be almost 

 wholly lost to science. He considered this a national calamity. 

 He hoped, for the honor of America, and the advancement of 

 science the world over that the edition would be so enlarged, that 

 every searcher after truth might obtain a copy. 



Afternoon Session — Friday, Sept. 24th. 

 On Heat, by Prof. Henry. 



He showed the analogy between light and heat, by stating that 

 as two rays of light might be so opposed as to produce darkness, 

 so two rays of heat might be so opposed as to produce cold; show- 

 ing that the theory of undulation is not an imagination, but the 

 expression of a law. The minimum of heat, as proved by his 

 experiments with the thermo-electric pile, does not correspond 

 with the minimum of light. Among flames, there are many which 

 give but little light, but which give great heat, as for example, 

 the flame of hydrogen. The amount of radiant heat and radiant 

 light were found to be about the same. 



The spots on the sun are colder than the surrounding surface; 

 and its surface is variously heated. This result he obtained by a 

 very simple experiment of throwing the disc of the sun on a 

 screen, and placing the very sensitive thermo-electric pile before 

 its different parts. He had not yet concluded his experiments on 

 the sun, and had not measured the comparative heating powers of 

 he centre and circumference, from which results very important 

 on sequences would be drawn. 



