[ 2T 4 ] 
XXX. M. de luc’s Rules , for the mea- 
furement of Heights by the Barometer , 
compared with Theory , reduced to 
English Meafures of Length , and adapted 
to Fahrenheit’s of the Thermometer : 
with Tables and Precepts , for expediting 
the praSlical Application of them. By 
Samuel Horfley, LL.D. addrejfed to 
Sir John Pringle, Bart . P. R. S- 
TO SIR JOHN PRINGLE, BART. P. R. S. 
S I R, 
Redde, Feb. i;,TN the papers which I have the honor 
1774 JL to prefent to you, nothing more 
was at firft intended, than to reduce the formula 
given by Mr. de luc, in his elaborate work 
upon the modifications of the atmofphere , for 
expreffing differences of elevation, as indicated 
by the barometer and thermometer, in Paris toifes, 
tt) others, which, from the like data , fhould ex- 
prefs fuch differences in Englifh fathom ; and at 
the fame time be adapted to that fcale of the ther- 
mometer, which is in general ufe in this country. 
Had I confined myfelf to this, which was my ori- 
ginal 
