156 THE ANTARCTIC MANUAL. 
In order to illustrate these remarks Table XX. has been con- 
structed. It is supposed that the barometer has been observed at a 
temperature of 0° C., and at the sea level in the latitudes given in 
the first column, and that it stands always at a height of 735°5 
millimetres. As the force of gravity at the sea level increases from 
the equator to the pole, this constant barometric height corre- 
sponds to a true atmospheric pressure, which increases as the pole is 
approached. This is given in the second column in grammes per 
square centimetre. In the third column these pressures are given in 
terms of the height of a column of mercury at 0° C. at the sea level, 
and in latitude 45°. In the fourth column the temperature of satu- 
rated steam, or the boiling-point of water under these true pressures is 
given. It will be seen that, other things being the same, the botling- 
point of water at the sca level is 0°°147 C. higher at the pole than at is 
at the equator. This figure is based on the assumption that the mass 
of the earth is homogeneous, or if heterogeneous, that it is symmet- 
rically heterogeneous with reference to its centre. It is also assumed 
throughout the whole of this argument, that there are no fluctuations 
in the atmosphere itself, and that the quantity of air in a column 
having unit area of base, at the sea level, is everywhere the same. 
TaBLe XX.—Givine THE TRUE ATMOSPHERIC PRESSURE AND THE BoiLtnc-Pornt oF 
Water CoRRESPONDING TO A Baromprric Hrieut or 735°5 MILLIMETRES AT 
0° C. anp at tur Spa LeveL In Dirrerent LArTITuDEs. 
Atinospheric Pressure. Corres- Atmospheric Pressure. Corres- 
ponding ponding 
Latitude, | Grammes Noa or ‘Skturated | Latitude, | Grammes ee ‘or Saturated 
siti, | tee. and | Steam, or the fete, | coma, pane 
Centimetre. Tate of Water. Centimetre. Graviey age} of Water. 
gr. p. cm?. mm. °C; i p. cm?, nm. ~ %. 
0° 1002°65 | 733°55 99-012 45° 1000°00 | 785°50 99° 087 
Jo° 1002°50 | 733-66 99°017 50° 999°54 | 735°84 99°099 
20° 1002°04 | 734-00 99° 029 60° 998°67 | 736°48 99° 123 
80° 1001°33 | 734°52 99°048 70° 997°80 73700 99°142 
40° 1000°46 | 735-16 99° 072 s0° 907°50 737° 34 99-155 
45° 1000°00 | 735-50 99° 087 90° 9U7°35 | 73745 99°159 
In the tabular example it is imagined that we carry a standard 
barometer from the equator to the pole, and that we read it at the sea 
level in certain latitudes, the barometer being entirely and exactly 
at the temperature of melting ice; and it is further imagined that 
the height of the barometer at each of these stations is found to be 
the same, namely, 755°5 millimetres. 
