Upon a REMARKABLE COLD. 171 



JANUARY 28. 1784. 



ABOUT nine o'clock this night, the excefs of cold was four, 

 five, and fometimes fix degrees. The circumftances of the wea- 

 ther, indeed, were now very particular. With the air fo warm 

 as +27, the fky was quite clear, whilft a ftrong wind blew di- 

 reclly from the north. At the fame time, too, the heavens 

 were illumined with a moft vivid difplay of the Aurora Borea- 

 lis, which (hooted from the north, round by the eaft, and up 

 beyond the zenith towards the fouth, where the wandering ir- 

 radiations all converged, fb as to form an imperfect crown. 



DURING this play of the elements, there were no longer to 

 be found the fmalleft traces of that hoar-froft about which I 

 had fo often been employed in calmer and in colder times. 

 Early in the afternoon, I had laid out a parcel of things, which 

 might fhow me the ftate of the air when night fliould come. 

 But neither upon them, nor upon the wooden fpars of the 

 wicket which opens from the fofle round the Obfervatory to the 

 park, nor upon its fide-flones, nor the hedge, nor the thorn- 

 tree near by, was there to be feen the fmalleft particle. Every 

 thing around was entirely gripped of hoar-froft by this dry and 

 devouring gale. 



THE fand-board and fnow-fcale, fet out as formerly, gave 

 now a very different report. The thermometer on the fand 

 never cooled a fraction of a degree below the temperature of 

 the air, whilft the fweeping wind cooled down the fnow feveral 

 degrees. Evaporation in all this was fo evidently concerned, 

 that it would have been abfurd to have tried if the fand had 

 loft weight in that way. But, at any rate, fuch an attempt 

 would have been difficult, as the fand was fo liable to be dif- 

 perfed by the wind, that I was obliged to lay it very thick upon 

 the fcale, and to flicker it a little under the lee of the hedge. 

 Being, however, defirous to know, at what rate the fnow wafted 

 by evaporation in this fituation, I got the white iron fcale, with 



Y 2 fnow 



