148 EXPERIMENT'S and OB SER VA TIONS 



The meets of paper, being thin and eafily cooled, acquired 

 it fooneft, and, when beheld by candle-light, were beauti- 

 ' fully fpangled over by innumerable reflexions from the mi- 

 1 nute cryftals of hoar-froft which had parted from the air. 



1 EVIDENT fymptoms of the fame difpofition of the air to 



' depofit hoar-froft occurred on all the former nights of ob- 



ferving, and the tubes of the thermometers were fo much 



1 crufted with it, that it required fome attention to keep that 



1 part which correfponded to the fcale quite free." At the end 



of faid paper is the following fcholium : 



THESE experiments, indeed, rather favour the opinion of 



1 the excefs of cold at prefent treated of, depending upon a 



principle the very reverfe of evaporation. But till opportu- 



' nities offer, in this, or in a colder climate, of making more 



' experiments, it will be too early to fay any thing very de- 



' cided concerning the nature and extent of a cooling procefs 



1 which has fo recently come under obfervation. All that can at 



1 prefent be affirmed is, that, in certain circumftances, fuch a 



1 procefs takes place ; and that it depends probably upon fome 



1 principles different from evaporation. At the fame time, fome 



" of the experiments fhow, that a free communication betwixt 



' the fnow and external air, perhaps whilft in motion, is ne- 



" ceffary ; but in what manner this promotes the refrigeration 



' does not as yet appear." 



THE experiments gone through this firft feafon, rendering it 

 fo difficult to account for the phenomenon by an evaporation 

 from the fnow, the next ftep was, to comprehend, if poffible, 

 by what other means fuch a cooling procefs could be maintain- 

 ed, confiftently with thofe general principles which were al- 

 ready known to have a real exiftence ; and to this point, I con- 

 fefs, I frequently turned my thoughts, from a fufpicion of there 

 being fomething fingular and undifcovered at bottom. 



ACCORDINGLY, before the return of the fucceeding winter, 

 feveral views occurred, concerning which it was propofed to 



make 



