WEIGHT OF AIR. 
785 
of air will be 
1-2930693 &-0-378IJ/ z 
1+0-003656^ 760 
1 — 0-0025659 COS 2X). 
In the cellar under the Mineralogical Museum in Cambridge, where tiie weights 
were compared, in lat. 52° 12' 18", about 8 metres above the mean level of the sea, 
this becomes 
1-293893 5-0-378W 
1+0-003656^ 760 
Since a litre is the volume of 1000 grammes of water at its maximum density, the 
above expression, divided by 1000, gives the ratio of the density of air to the maximum 
density of water. The logarithm of the ratio of the density of air at t°, to the maxi- 
mum density of water, is obtained by adding the logarithm of b—0’S78v in milli- 
metres to log At. 
Table I. 
(. 
0 
1 
2 
.3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
10+log 1-293893 — 3-log 760 — log (1 -1-0-003656 t). 
10+ log Af . 
4-231083 
4-229500 
4-227921 
4-226347 
4-224780 
4-223217 
4-221661 
4-220110 
4-218565 
4-217025 
4-213490 
4-213961 
4-212437 
4-210919 
4-209406 
4-207898 
Diff. 
1585 
1579 
1574 
1567 
1563 
1556 
1551 
•545 
1540 
•535 
1529 
1524 
1518 
•513 
1508 
t . 
10+log Af . 
15 
4-207898 
16 
4-206396 
17 
4-204898 
18 
4-203406 
19 
4-201919 
20 
4-200436 
21 
4-198959 
22 
4-197488 
23 
4-196020 
24 
4-194538 
25 
4-193101 
26 
4-191648 
27 
4-190201 
28 
4-188758 
29 
4-187320 
30 
4-185887 
DifF. 
1 502 
1498 
1492 
1487 
1483 
1477 
1471 
1468 
1462 
1457 
1452 
•447 
•443 
•438 
•433 
The logarithms in the preceding Table, when diminished by 0-000028, serve for the 
reduction of the weighings in Somerset House, lat. 51° 30' 40", 29*56 metres above the 
mean level of the sea; and when diminished by 0-000132, they may be used for the 
reduction of weighings in Paris. 
According to a document to which the names of Biot, Regnault, and Bianchi are 
appended*, the pressure of vapour in rooms that are not heated artificially, in Paris, 
is two-thirds of the maximum pressure due to the temperature. It is probable that 
in Cambridge the hygrometric condition of the air is very nearly the same. 
* Memorie di Matematica e di Fisica della Societa Italiana della Scienze residente in Modena, tomo 
XXV. p. 1. 
