C 2*5 ] 
ginal defign, I fhould certainly have fupprefled what- 
ever I might have executed, as I find my learned 
friend the astronomer royal hath devoted 
fome of his leifure hours to thefe calculations ; and 
the redudtions, I propofed, are actually performed, 
in a fhort and elegant paper of his upon the fubjedt, 
which is already, I believe, in Dr. maty’s hands. 
But I had made but a fmall progrefs in my intended 
work, when it occurred to me, that tables of the 
equations for the effects of heat and cold, would be 
very ufeful. Such I have taken the pains to con- 
ftrudt, and have carried them to as great a length, 
as can be ever wanted. They are annexed to 
the enfuing piece, and will render the application of 
Mr. de luc’s rules more eafy and expeditious, than 
any peculiar divifions of the thermometrical fcale. 
When my tables were finifhed, I thought it might 
be flill further ufeful, to give a fuccindt explanation 
of Mr. de luc’s orignal formulae ; that fuch as have 
not leifure to perufe his excellent work, might be 
furnilhed with a competent idea of the refult of his 
refearches. This, I found, I could not do, in any 
way fo fatisfadtory to myfelf, as by opening, as I 
went along, the principles of theory, in which the 
conclufions, he hath arrived at, appear to originate. 
And thus 1 was infenfibly led into minute difquiii- 
tions, concerning the agreement of Mr. de luc’s 
conclufions, from a long train of accurate experi- 
ments, with the geometrical theory of the atmo- 
fphere, founded on the general laws of gravitation. 
In this manner, sir, the papers before you have 
taken, as it were fpontaneoufly, the form, in which 
they now appear j and a fubjedl, remotely connedted 
with 
