344 CONGELATION. 



air ; but the vessel on the window sole remained perfectly- 

 fluid, and the flask on the neighbouring cherry tree was 

 only^ wet with dew, being untouched by hoar frost. 

 The Parisian Several of the facts stated above are common occur- 



cxpenments r^nces, and they seem to reconcile the opposite results of 



were probably ' •' ' ' * 



made in favor- my experiment with ease ; we may therefore say, with- 



able cir<?um- ^^^ hesitation, that the experiments of the Parisian philo- 



sopher happened to be made under circumstances which 



proved highly favourable to his hypothesis. I venture to 



make this assertion, because a saucer of water, one half 



of which was covered with glass, cvidentify comprises all 



his experiments in one ; it also refutes them singly, by 



shewing that congelation took place under the pane, of 



glass, as well as in the exposed part of the saucer. In 



order, however, to give an additional proof of a fact, 



which is almost demonstrated by common observation, I 



took the opportunity of a calm evening when the frost 



was very gentle, and placed a Cup of water under a glass 



bell upon a stand in the middle of the garden ; at the 



same time a circular plate of metal, five inches in diameter, 



was suspended horizontally over the centre of a vessel of 



water, which was considerably broader than itself; the 



distance between the plate and water M'as about two 



inches, but neither the bell nor the plate prevented their 



Water will respective vessels from being covered with ice. It will 

 treeze under a ^ „ , , , . . . i • n • 



cover. now appear, that congelation is not caused m Sprmg and 



Autumn by adventitious particles of any kind falling 

 from the atmosphere ; on the contrary, vernal and 

 autu'niiial frosts must evidently be ascribed to the com- 

 mon effect which is universally produced in water by a 

 temperature less than 32°. Wh'at is still more to the 

 - present purpose, wat6r may be cohcreted into ice, in 

 circumstances under which the aqueous part of the at- 

 mosphere cannot be converted into hoar frost ; so that 

 there isTio necessity to employ the latter production as 

 an agent contributing to the formation of the other. 

 The truth' of what is here advanced will be proved by the 

 following experiment, which I made some years ago;— ■ 

 Congelation in Having observed a quantity of wet woollen yarn to be 

 circumstances frozen, whioh was exposed to a moderate north wind 

 f>o6^t' could not "PO" *^c ^'^^^^ ^^ ^ wooden bridge, 1 suspended a ther- 

 be formed. mometer 



