VOL. XLIV.] PHILOSOPHICAL TRANSACTIONS. 401 



barometer at the same time, to determine the degrees of heat at a great distance 

 of time between each experiment. 



The most usual kind of thermometers, is that described in the account of the 

 experiments by the academy of Cemento ; which being the common ones, made 

 of spirit of wine tinged, it is needless to describe. The bounds of the degrees 

 of heat which these will measure, and which is commonly called the range of 

 the instrument, are from the degree which freezes spirit of wine, up to that which 

 • makes it boil. The spirit-thermometers, commonly made here in London, are so 

 graduated, that when the spirit is rarefied to the degree that the most sultry sun- 

 shine, commonly known in our climate of 51-^° n. lat. can raise it, there is placed 

 the mark O, or degree of no cold. Some few are marked ] O or 20 above this, 

 when intended to be used in hotter climates; but all are graduated downwards 

 from this: so that 45° is the point of temperate, and 65° the point of freezing, 

 and 100° is placed just above the ball. But the most accurate spirit-thermometers, 

 are those lately made by M. Reaumur, member of the Royal Academy of 

 Sciences at Paris ; he has taken a great deal of pains and used great exactness, in 

 fixing the certain points of freezing of water, of temperate air, and of boiling 

 water. He determines the freezing point, by leaving his thermometer a consi- 

 derable time in water, into which is put a good deal of ice, at a time when the 

 water would not freeze of itself; and this he marks O, or the degree of no heat; 

 and his scale is marked with numbers running downwards from O, measuring the 

 degrees of cold, and upwards measuring the degrees of heat: at 10^ upwards he 

 marks the point of temperate, which he determines by placing his instrument in 

 a subterranean cavern, which is neither affected by frost nor sunshine, but is ob- 

 served to keep an equable temperature all the year round; such as deep cellars 

 and wine vaults commonly do. In boiling water he finds that his thermometer 

 rises to his 80th division,* or 80 degrees, which are formed by dividing the 

 spirit when condensed to the freezing point, into 1000 equal parts; so that, with 

 the heat which makes water boil, the spirit is expanded only , gg^ more than with 

 the cold which freezes water. 



These spirit-thermometers are of use in experiments where somewhat greater 

 cold than the freezing of water is required; but they can never be of use in 

 any degrees of heat beyond the boiling of the spirit itself; because it then be- 

 comes volatile, or rises up in steam, and not only expands no more, but likewise 

 the quantity is diminished by the particles which fly up from the surface of the 

 liquor, and are suspended in the top of the tube. 



• But, with submission to so great a man, 1 cannot apprehend that his thermometers, when the 

 spirits are raised up to 80, do mark any greater degree of heat than their own specific boiling heat, 

 which, if they be alcohol, or the most rectified spririts, answer to 174 of Fahrenheit's scale; if of the 

 strength of common brandy, to IQO. — Orig. 



VOL. IX. 3 F 



