PROCEEDINGS OF THE TOLYTECHNIC ASSOCIATION. 323 



a dozcMi stones in the form of a boy's marble, and he distinctly recoUecled 

 tliat otliers gatliered by him liad a conical shape. 



Dr. W. Kowell rcineinbered the storm alluded to ; the shape of some of 

 the hailstones which fell in Bleecker street was peculiar, resembling some- 

 what a rough oyster shell. 



Mr. J. M. Root remarked that he had witnessed the most severe hail- 

 storm probably on record. It occurred about the 10th of June, 1849, on 

 the groat plains, some 50 miles east of Fort Laramie, Nebraska Territory. 

 Some of the stones which fell measured fourteen inches in circumference. 

 They were composed of solid ice, about the size of a hen's egg, with 

 smaller portions adiiering to them. He noticed that some of these hail- 

 stones were of conical form and onl}^ about three inches in circumference. 

 Several persons in this party were injured in this storm. One man had his 

 skull fractured, another his arm broken. The skins of animals exposed 

 were cut through. The covers of their wagons, sustained by hickory 

 frame-work two inches thick, could not resist the force. The hail-storni 

 lasted from ten to fifteen minutes. 



It would be inferred from the further debate, that hailstones of a conical 

 form were not a novelty in this country. 



Cooling of Solids by Tension. 



Mr. James Croell, in the May number of Tlie Philosophical Magazine,^ 

 directs attention to the experiments of Dr. Joule, which proved tht^t the 

 quantity of cold produced by the application of tension to solids was sensi- 

 bly equal to tjie heat evolved by its removal; and further, that the thermal 

 effects were proportional to the weight employed. The probable explana- 

 tion given by Mr. Croell is this: If the molecules of a body are held together 

 by any force, of whatever nature it may be, which prevents any further 

 separation taking place, then the entirejieat of such a body will appear as 

 temperature; but if this binding force become lessened, so as to allow fur- 

 ther expansion, then a portion of the heat will be lost in producing expan- 

 sion. All solids, at any given temperature, expand until the expansive 

 fijrce of their heat exactly balances the cohesive force of their molecules; 

 after which no further expansion at the same temperature can possibly 

 take place while the cohesive force remains unchanged. But if by some 

 means or other the cohesive force of the molecules becomes reduced, then 

 instantly the body will expand under the heat which it possesses, and of 

 course a portion of the heat will be consumed in expansion, and a cooling 

 effect will result. 



Actinism from Different Parts of the Sun's Disc. 



Sacchi having shown that the heat radiated from the center of tiie sun is 

 nearly double that from its borders, and that the equatorial regions are 

 somewhat hotter than the polar, and various observers having noticed a 

 great difference in luminosity between the center and the edge of the disc, 

 Mr. II. E. Roscoe now reports to the Royal Society some experiments made 

 by means of photographic paj)er relative to tlie chemical action of rays from 

 various parts of the sun's disc. From the results of one day, it appears 



