CHEMICAL AND PHYSICAL NOTES. 99 
This table shows how rapidly the tension of saturated steam rises, 
as compared with its temperature. It also shows that the lower the 
tension of the steam, the more efficient is the thermometer for indi- 
cating it. But, for hypsometric purposes, it must be remembered 
that the higher we climb on a mountain the greater is the height 
required to produce a given fall of the barometer. 
That these two effects very nearly compensate each other is shown 
in Tables V. and VI.,* which give the temperature of boiling 
TapLe V.—Givine THE Tension or SaturatTep Stream in Millimetres and Inches, and 
the Corresponpinc HeIGHTS aBOVE THE Sea in Metres and Feet, for TrmPERa- 
TURES in CELsIus degrees. 
temp Barometric Pressure. Height above Sea-Level. 
Saturated 
Steam. Millimetres. Inches. Metres. Feet. 
° Celsius. 
85 433-0 ag 17°05 as 4495 oe 14,750 oe 
86 450°3 17°3 17°73 0°68 4182 313 13,734 1016 
87 468 °2 179 18°43 0°70 3871 311 12,724 1010 
88 486°6 18°4 19°16 0°73 3562 309 11,718 1006 
89 505°7 19°1 JeaL 0°75 3255 307 10,717 1001 
90 525°4 19°7 20°69 0°78 2990 305 9,720 997 
91 545°7 20°3 21°48 0:79 2647 303 8,728 992 
92 566°7 21:0 22°31 0°83 2345 302 7,740 988 
93 588°3 21°6 23°16 0°85 2045 300 6,757 983 
94 610°7 22° 4% 24°04 0°88 1747 298 5,778 979 
95 633°7 23°0 24°95 Wesel 1451 296 4,804 974 
96 657°4 23°7 25°88 0°93 1157 294 3,834 970 
97 681°9 24°5 26°85 0°97 865 292 2,869 965 
98 707°2 25°3 27°84 0°99 575, 290 1,908 961 
99 733°2 26°0 28°87 1°03 287 288 952 956 
100 760°0 26°8 29°02 1:05 0 287 0 952 
water in Celsius degrees in Table V., and in Fahrenheit degrees in 
Table VI., and the barometric pressure, in inches and millimetres, 
which is equal to the tension of saturated steam at the particular 
temperature, with the height above the sea, in metres and feet, at 
which this barometric pressure would be found in a still dry atmo- 
sphere at the temperature of melting ice. It will be seen that 
throughout a range of 4500 metres, or 15,000 feet, a depression of 
the boiling-point by 1° C. corresponds very closely to an ascent of 
300 metres, or 1000 feet. If the column of differences of the baro- 
* These tables are compiled from Tubles 20, 25, 33 and 34 of the Smithsonian 
Meteorological Tables, 1893. No. 844 of the Smithsonian Miscellaneous Collections, 
H 2 
