402 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747, 



Many have filled their thermometers with various sorts of oils:* these indeed 

 will measure many degrees above the boiling of water, till they boil themselves; 

 and then they have the same defect as the spirit ones just mentioned, which is the 

 liquor losing of its bulk by evaporation ; and they congeal much sooner than 

 water, and so are useless in measuring any degrees of cold. 



The most useful instruments, as they comprehend the largest range, are the 

 mercurial thermometers, brought into use by that ingenious artificer Fahrenheit, 

 p.R.s, See Phil. Trans. N° 381 : but to do justice to a most worthy member of 

 the Royal Society, viz. Dr. Halley, he first gave the hint, and even proposed 

 the making thermometers of quicksilver long before Fahrenheit's time, see Phil. 

 Trans. N° I97. However, Fahrenheit deserves thanks from the world for having 

 brought these instruments into use, because they will measure the greatest degrees 

 of cold yet known; for no cold hitherto observed has been able to freeze or ren- 

 der mercury solid :-f- and in measuring heat, they go far beyond boiling water, 

 even beyond the melting of tin or lead. Fahrenheit begins his scale from O, the 

 point to which the mercury has been observed to fall by the greatest cold in 

 Ysland; and computes, that the mercury then;}: occupies 11124 parts. This is 

 his point of no heat. Then reckoning upward from this, he finds that when the 

 mercury is rarefied only 32 parts or degrees more, common water just begins to 

 freeze: in a temperate air it will rise to about 60. The most sultry sunshine 

 seldom raises it to 90 ; the heat of an animal body to g6, the boiling of alcohol 

 to 174; the boiling of water to 212; and before the mercury itself boils, it will 

 rise to 600. 



The following curious and surprising experiment of Fahrenheit's, concerning 

 the artificial production of cold is related by Boerhaave, is his Chemistry, Tom. I. 

 p. 164. Fahrenheit had a mercurial thermometer made with so long a stem, that 

 he could carry down the scale 76 parts or degrees below O. With this instru- 

 ment he found, that cold might be produced by gradually pouring spirit of nitre 

 on powdered ice, till the mercury would subside to 40° below O, that is 72° § lower 

 than the cold which freezes common water. Boerhaave, ib. p. 161, mentions 

 a very pretty way of determining the freezing point: he advises to hang the 

 thermometer free in the open air, not against any wall or building; and near it 

 hang a piece of very fine linen or muslin just dipped in clean water: when this 

 begins to grow stiff, you will find the mercury stand at about the 33d degree; and 



• See Dr. Martin's essays Med. and Pbilos. p. 225. Sir I. Newton's thermometer was made of 

 linseed oil. See his scale of heat, Phil. Trans. N" 270, p. 82*. — Orig. 



+ That this has since been done, will appear, in a future volume of the Transactions. 



X SeeBoerh. Chem. Tom. I, p. 174.— Orig. 



§ But what is this to the marvellous natural cold of Siberia, 120° below 0? See the preface to 

 Gmelin's Flora Siberica. — Orig. 



