[ 682 ] 
of Water to 2125 and before the Mercury itfelf 
boils, it will rife to 600. 
I cannot here forbear giving an Abftra&of a very 
curious and furprifing Experiment of Fahrenheit's , 
concerning the artificial Produftion of Cold, as it is 
related by Boerhaave in his Chemijlry, Tom. I.p. 164. 
Fahrenheit had a Mercurial Thermometer made with 
fo long a Stem, that he could carry down the Scale 
76 Parts or Degrees below o. With: this Infirm 
ment he found, that Cold might be produced by 
gradually pouring Spirit of Nitre upon powder'd 
Ice, till the Mercury would fubfide to 40° below o. 
that is 72 0 * lower than the Cold which freezes com- 
mon Water. Boerhaave , in his Chemijtry, Tom. I. 
p. 1 6 1. mentions a very pretty Way of determining 
the freezing Point: He advifes to hang the Thermo- 
meter free in the open Air, not againft any Wall 
or Building ; and near it you mull hang a Piece of 
very fine Linen or Muflin juft dipp'd in clean Wa- 
ter : When this begins to grow ftifr, you will find 
the Mercury ftand at about the 33 d Degree 5 and it 
will alfo ftand at the fame Height when an hoar 
Froft appears upon the Ground 5 which he looks 
upon as a certain Sign of the Beginning of freezing. 
Having thus given an Account of the feveral Sorts 
of Thermometers hitherto ufed, and what Degrees of 
Heat they are proper to meafure, we find none of 
them capable of meafuring the greater Degrees 
of Heat, which are the mod commonly made ufe 
of 
* Bat what is this to the marvellous natural Cold of Siberia, 120°. be- 
low o ? See the Preface to Gmclin ' s Flora Siberica. Petrop . 1747. 4 to* 
