756 Col. roy’s Experiments for 
will, always meafure the equations applicable in the rc- 
fpeftive fituations. The equatorial curve will probably 
change the faff eft, and the others become gradually flat- 
ter, as they approach towards the poles, where the 
greater, but more uniform, denfity of the atmolphere 
may occafion it to differ little from a ftraight line. I ap- 
prehend, however, that even at the pole fome fmall di- 
minution might be found to take place in the equation, 
was it poflible, in that region, to prove it by experiments 
at a fufflcient height above the level of the fea. 
The table of the equation, depending on the heat of 
the air, annexed to this paper, is conftrudted for middle 
latitudes. It extends to temperatures from 1 2° to 92° of 
Fahrenheit; and for fituations fo greatly elevated 
above the fea, as to make the mean barometer between 
the two ftations ftancl no higher than 19 inches. As the 
equation correfponding to the lower parts of the atmo- 
fphere, contained in the right-hand columns, will come 
more frequently into ufe than that appertaining to the 
higher regions, comprehended in thofe on the left; 
therefore, in the firft, it is given for every half; and in 
the laft only, for every whole inch of defcent of quick- 
lilver in the tube. 
1 he equation found in the column of 29 inches, cor- 
xefponds exactly with the expanfion of air refulting from 
the 
1 
