Miscellanies. 39? 



the top so as to receive a certain quantity of liquid, and thus to meas- 

 ure its temperature as it evaporates. He concludes from his experi- 

 ments vidth water, that a prompt evaporation produces cold even un- 

 der the immediate influence of the sun's rays ; and from experiments 

 with spirits of wine, he draws the conclusion that the temperature of 

 a liquid which is evaporating, can rise only when the evaporation is 

 slow. There is then, he observes, no" doubt that the cause of the 

 primitive formation of hail lies in the prompt evaporation of the little 

 globules of which the clouds are formed. Occupied exclusively with 

 electricity, Volta (says Prof. P.) lost sight of the principal cause of 

 the refrigeration of the clouds, and the laminated structure of hail 

 stones. The following is the explanation of the Russian philosopher* 

 " When clouds are formed of several thick strata, gradually ascendingj 

 they form an obstacle to the free distribution of radiant heat, which, 

 being reflected to the earth, produces that suflfocating heat which com- 

 monly precedes a storm. At the same time, the sky, above the 

 cloudSj being perfectly serene, presents no obstacle to the radiant heat, 

 which emanates freely from their upper surface. Hence, the princi- 

 pal cause of their congelation, on which depends the formation of the 

 nucleus of the hail stone. The specific weight of those nuclei, not 

 allowing them to remain suspended in the cloud, they fall, and trav- 

 ersing different beds of cloud, they become enveloped with successive 

 coats of congealed fluid, corresponding with the number of strata 

 through which they have passed. These hail stones may acquire, by 

 collision, a rotatory motion, which gives them their spherical form." 

 From these views, the author infers the uselessnesSj and even danger, 

 of paragreles.— Sz&. Univ. Aoiit, 1830- 



13. Expansion of Gases. — If a musket be loaded with a ball, the 

 flight of the latter may be prevented by the pressure of a finger on 

 the ramrod resting on the ball. This is accounted for on the princi- 

 ple, that at first the ball ha,3 a feeble velocity, compared Avith that 

 which it speedily gains by the expansion of the gases, which contin* 

 ues throughout the tube. Hence a long tube carries a ball so much 

 farther than a short one, and hence also a puflffrom the mouth, which, 

 as it issues from the lips, has the force of not more than \ of an at- 

 mosphere, can drive a ball sixty paces when blown from a sarbacane. 

 The experiment first mentioned requires great caution, for the gun is 

 apt to burst. — Ihid. 



14. Leonardi da Vinci. — In the tenth volume of the fourth edition of 

 the collection of Italian authors, published at Bologna in 1828, is a 



Vol. XIX.— No. 2. 51 



