1819.] and the Specific Gravity of Atmospheric Air 343 
And the weight of the same sphere in air at 
67° and 29-74 by first trial. ... = 28722-6400 
Cor. for error from buoyancy.. — 00000-0467 
——  28722:5933 
68° and 30-13 by second trial. = 28721-8800 
For diff. in therm. and barom. + 00000-3769 
Error from buoyancy. ...... — 00000-0915 
—-——__ 287221654 
Same, by third trial. ..- swsapimea---2¢++s2. 20120 One 
Mean...... 28722-3080 
From which take the mean weight of the sphere 
Grains. 
I WateE oe esse ecesee Snime © bap hdsehhe «« — 00049-2590. 
Weight of a bulk of water = the sphere at 
OO BN OTe oe cc conten gs sgecw mens 28673-0490 
— 00000-3063 
66 and 30:00 ...... oLepws OS Jee alg wees 128672°7427 
28672°T427 , : st his 
. — 959- 
ioe ee 262580 is the weight of a cubic inch of distilled 
water at 66° and 30. But as the weights used were too light, 
when compared with the Exchequer standard, by | in 1523-92, 
that quantity must be deducted ; leaving 252°414 gr. standard ; 
correcting for expansion of water 0°99939 : 1 :: 252-414 ; 252°568 
at 60° and 30. Now in this state of the atmosphere, it displaces 
a volume of air = 0°30519 gr.; but at 66° and 30 = 0:30161 ; 
~. 252-568 being diminished by the difference 0°00358, gives 
252564 for the weight of a cubic inch of distilled water at a 
mean temperature.and pressure. If we suppose the water used 
in the different trials to be a little impure, so that its specific 
gravity at 60° = 1000138, we shall have 252°529 as the true 
weight in standard grains of a cubic inch of the purest distilled 
water, in a temperature of 60° and under a pressure of JO in. 
This numbers differs but very little from 252°525. 
The reason for pitching on the number 1:000138 to represent 
the specific gravity is, that Sir George Shuckburgh, after one of 
his experiments, found the distilled water used to weigh at 60° 
1-00055, allowing half the increase indicated by the hydrometer 
to be caused by inaccuracy in the instrument, and half the 
remainder for impurity contracted subsequently to the experi- 
ment, we shall find 0:000138 as the increase in specific gravity 
to be corrected for. 
In the commencement of this paper, I mentioned that the 
number 252°525 possessed the advantage of convenience ; it is 
particularly obvious in calculating the weights of any determi- 
nate volume of a body, whose specific gravity in relation to 
water we have given. I shall just state an example of the ope- 
