CHEMICAL AND PHYSICAL NOTES. 157 
If we assume that the force of gravity is the same at the sea 
level in all latitudes, then the fact that the atmosphere everywhere 
exercises the same pressure as a certain standard length of mercury, 
is evidence that the mass or the quantity of air in a column of the 
atmosphere having the same base is, at the sea level, everywhere the 
same. If the height of the standard barometer had not been the 
same at each of these stations, and at the same time it was known 
that the force of gravity did not vary, then the conclusion would be 
necessary that the quantity of air in the atmosphevic column at the 
sea level is greater in one latitude than in another. 
If the height of the standard barometer is, as postulated in the 
table, the same at each of the stations, and if it is known that the 
force of gravity is not constant, then the height of the standard 
barometer of itself gives us no information regarding the pressure of 
the atmosphere. The constancy of the height of the standard baro- 
meter justifies no other conclusion than that the pressure of the 
atmosphere is different in different latitudes. 
If the law of the variation of the force of gravity with change of 
latitude is known, then the constant height of the barometer allows 
us to arrive at the relative pressure of the atmosphere at different 
latitudes. If, in addition, the absolute value of the force of gravity 
at any one latitude is known, the constant height of the standard 
barometer enables us to conclude what is the absolute peer of the 
atmosphere at the different latitudes. 
If the distribution of matter in the earth is homogeneous, and if 
the force of gravity at the sea level varies, then the conclusion is 
necessary that different stations at the sea level are at different dis- 
tances from the centre of the earth, or they are at different altitudes, 
referred to this point as fundamental datum. 
If the law which connects the variation of the force of gravity 
with distance from the attracting centre is known, the distance of the 
sea level in any locality from the centre of the earth is at once ascer- 
tained by determing the force of gravity there ; hence the gravitational 
method of determining the figure of the earth. Here it must be 
remarked that a perfect survey of the figure of the earth may be given 
without affording any information about its size. 
To return to the barometric data in the table, we see that while 
the height of our standard barometer was the same, 735°5 mm. at 
every station, the indications of the hypsometer or the boiling-point 
varied. It has been shown that the height of the barometer is not 
affected by change in the force of gravity, but that the pressure of the 
atmosphere is so affected ; we might conclude that in the temperature 
