in order to afcertain the height of Mountains. 581 
This laft obfervation was actually made, and the 
height geometrically was determined to be 421 1.3 feet, 
not quite two feet different. In this example it will be ob- 
ferved, that as the height of the barometer is fet down to 
four places of decimals; the tabular numbers, anfwering 
to every tenth only, are corrected by means of table III. 
of proportional parts, for the remaining decimals 8, 9, 
and 2, in one place; and 3, 1, 8, in the other; and their 
fum is fubducted from the numbers found in table II. 
And laftly, that in finding the correction for 2 8°. 7 of 
heat, the fraction fz is confidered as fo many units, and 
another decimal is ftruck off; thus the correction on 
3000 feet for 7 0 is 51; but for ^ it becomes 5.1, and 
fo of the reft. 
EXAMPLE III. 
In the upper gallery of the dome of St, Peter’s church 
at Rome, and 5 o feet below the top of the crofs, I ob- 
ferved the barometer, from a mean of feveral obferva- 
tions, 29.5218; the thermometer attached being at 
56°. 6, and the detached one at 57 0 ; at the fame time 
that another, placed on the banks of the Tyber one foot 
above the furface of the water, flood at 30.0168, the 
attached thermometer at 6o°.6, and the detached one at 
6 o °.2; what was the total height of this building above 
the level of the river? 
Obfer- 
