1864.] 457 [Zantedeschi. 



always greater .than that from the supersaturation of the air; and 

 that from the evaporation from plants was always less. The experi- 

 ment seems entirely new and decisive. 



I studied with repeated and laborious experiments to determine 

 the source of the cold necessary for condensing the aqueous vapor 

 forming dew and hoarfrost. By comparative observations I have 

 convinced myself, that the frost of the air precedes that of the moist 

 solids, and that the moist solids do not chill below the temperature 

 of the circumstanding air, taken at the mean height, always in calm 

 and serene nights. It was made apparent by my vertical balance 

 Anemoscope that the nocturnal frost derived itself from the column 

 of cold descending air. I recognized the fact that the surface of the 

 soil, and even of the snow covering it, is always colder than the stra- 

 tum of air above it ; and that with every departure from this stratum 

 the temperature of the air is increased. In all these facts, I have 

 done justice to all the physicists who have preceded me, and I i*egis- 

 ter that which is granted to my observations and experiments from 

 my friends. 



I have not forgotten to verify the influence exerted by electricity 

 on the deposition of aqueous vapor on solids. I finish these my 

 letters, with two useful applications to Agriculture and to Hygiene, 

 always under guidance of history and experience. 



I beg physicists living in the open country in serene and calm 

 nights to repeat all these observations, which complete the theory of 

 the dew and the hoarfrost. May this, my request, obtain favor from 

 your honorable Society, to which, I declare myself with the highest 

 esteem and perfect observance, Zantedeschi. 



Padova, September 11th, 1864. 



An enamelled portrait of a French gentleman, concealed 

 in the bottom of an inkstand or wafer-box, and thrown out 

 by the workmen in digging the foundation for an enlarge- 

 ment of a house, originally built in 1785, at Valley Forge (the 

 headquarters of General Washington, in the winter of 1776), 

 was exhibited to the members by Mr. T. P. James. The relic 

 is, apparently, a work of art of the age of Louis XVI ; and 

 much pains has been fruitlessly expended for its identifica- 

 tion, both in Europe and in this country. 

 VOL. IX. — .Si 



