[ *58 ] 
XX. M. De Luc’s Rule for meafuringH eights 
by the Barometer , reduced to the Englifli 
Meafure of Length , and adapted to Fah- 
renheit’s Thermometer , and other Scales 
of Heat, and reduced to a more conve- 
nient Exprejfon . By the Afronomer 
Royal . 
Rcdde, Jan. "ft, /r de luc, f. r. s. in a large and 
J 3> 1 774- valuable Treat ife upon the Ba- 
rometer and Thermometer, lately published at 
Geneva, the relult of many years labour and 
Siudy, has given a rule for the meafurement of 
heights by the barometer, deduced from his ex- 
periments, and far more accurate, than any pub- 
lished before ; iince it appears that he could 
determine heights by it generally to ro or 
15 feet, and that the error feldom, if ever, 
amounted to double that quantity. This valuable 
degree of exadtnefs he has obtained principally 
by detecting the faults of the common barometer, 
and, in confequence, improving the construc- 
tion of it j and by introducing the ufe of the 
mercurial thermometer, to accompany that of 
the barometer. The principal faults, which 
he found in the common barometers, arofe from 
2 the 
