Upon a REMARKABLE COLD. 155 



WITH a view to fome more exact ftatical experiments than 

 thofe made in the year 1781, I had now prepared a flat circu- 

 lar fcale, made of white iron, two feet in diameter, and turned 

 up at the circumference about half an inch. In place of cords 

 for hanging it to the balance, it was found more commodious 

 to fubflitute pretty ftrong wires, by which the fcale could be 

 lifted up and fet down, and carried backwards and forwards, 

 without ever interfering with the fnow upon its furface, as 

 fometimes was the cafe when cords were ufed on former occa- 

 fions. This fcale was covered with fnow quite to the brim, 

 and, when cooled in die open air, it was applied to a good ba- 

 lance, and exactly counterpoifed, by adding at lafl to the oppo- 

 fite fcale very fmall drops of lead-fhot. That no part of the 

 external furface of the fcale might communicate with the air, 

 it was placed upon a round board, which had in "it a circular 

 fpace, juft deep enough to receive the fcale up to the brim. In 

 this ftate, where nothing, therefore, but the fnow which co- 

 vered it communicated with the air, it was expofed abroad 

 four feet from the ground upon a fmall table, at nine o'clock. 



NOT only by repeated trials of the weight of this fcale, but 

 alfo by clofe infpection by candle-light, I wanted to determine 

 at what times the air was depofiting hoar-froft, or taking the 

 fame up in the way of evaporation ; and particularly to mark 

 the connection betwixt thefe contrary dates of the air in the 

 lower regions and a ferene or clouded atmofphere, upon which 

 lafl the variable temperature at the furface of the fnow feemed 

 fo immediately to depend. 



FOR this purpofe, befides the fnow-fcale, there were expofed 

 a variety of bodies, fuch as glafs, metal plates, meets of dark 

 coloured paper, a plank of wood, china, &c. 



UPON frequently examining all thefe bodies by candle-light, 

 from nine o'clock till twenty minutes pad eleven, it was quite 

 manifeft, that they were drawing hoar-froft from the air, and 

 in the fame order as is mentioned in the quotation from the ex- 



U 2 periments 



