the Meafurement of Heights with the Barometer. 687 
the equator, I fhould be extremely cautious how I ad- 
mitted a latitudinal equation ; nor do I think the tingle 
obfervation, related in Phe Voyage towards the North 
Poky of fufficient authority itfelf to eftablifh fuch a 
theory upon %. 
them vve are fbill more at a lofs, having a range of no lefs than 38° to aflame 
it in (vide Voyage au Per u, p. 29.). The mean, however, of his five obfer- 
tions, according to my computation, would bring the zero of the fcale to about 
40° of Fahrenheit: but till it can be proved, that in this uncertainty of 
38° vve have, in fixing upon the mean, got the true temperature to within 8®; 
and aifo, that during many months the barometer in the fame place had never 
altered a fingle line: till then, I fay, no fair conclufion, in point of theory, 
can be drawn from thefe experiments, for with fuch fuppofed errors or varia- 
tions the Peruvian observations will agree exa&ly with tliofe in this climate. 
(h) It feems extraordinary, that the heights of the quicklilver, obferved on 
the fea-fhore with one of Mr. ramsden’s barometers, fhould differ a quarter 
of an inch from the height of the fame obferved the fame day, and almoft at 
the fame hour, with Mr. nairne’s marine barometer on board a fhip (vide p. 
135 and 148. of The Voyage towards the North Pole), This difference, there- 
fore, I think remains to be explained, if the experiment is to be made ufe of in 
this inquiry; for this fame marine barometer, compared a few days ago at Mr. 
ibbetsqn’s, fecretary to the board of longitude, with one of my own, that I ufed 
in Savoy, agreed with it to within 0,04 inch. It may alfo be remarked, that 
Lord mulgrave’s obfervation in lat. 79 0 44' brings the zero to about 64°; fo 
that between the lat. 56° and 79 0 (equal a$°) the zero of the fcale moves 
through afpace of no lefs than 32°; whereas, between the lat. 46° and 56° it is 
perfe&ly flationary, at leaft as to fenfe, having altered only one-third of a 
degree: which great want of proportion, I think, is of itfelf fome argumen c 
againft the exiftence of fuch a latitudinal equation. Moreover, Mr. bouguer's 
obfervations brings the zero of the fcale on the fame fide of 3 2 ° with Lord 
mulgrave’s, viz . to about 40°, fo that, if any deduction is to he drawn from 
thefe obfervations, it is, that the air, both at the equator and at the pole is heavier 
than in middle latitudes, which is no very probable conjie&ure, and, I appre- 
hend, more than is intended to be proved. I fhould have rdked pardon for the 
freedom with which I have difcuffed this inquiry, were I not allured chat the 
acquaintance and friendfhip of my Lord mulgrave, which 1 have experienced 
for fome years, will lead him to attribute it to its proper motive. 
T 
