198 Table for ascertaining the Heights of ~ [Aprit, 
on some standard thermometers in the Surveyor General’s office, in our 
experiments on the standard bar, we found the boiling point erroneous 
two degrees: and Lieut. Burnes found his thermometer boil on the 
Caspian Sea at 21303 which would make its surface 700 feet below the 
level of the Mediterranean, whereas it is only suspected of half that 
depression. 
2. The metal or wooden scale should be cut off at some height above 
the bulb, as otherwise it is very difficult to obtain the temperature cor- 
rectly, oreven to attain full ebullition, on account of the rapid abstrac- 
tion of heat by the scale, particularly if it be of metal. 
8. The vessel in which the water is boiled should be of metal, 
closed loosely with a cover or cork through which the thermometer 
may pass, so that the bulb may remain a trifle above the surface of the 
water. To those who cannot provide themselves with a boiler similar 
to that of WotLasTon, a shaving pot will be found to answer sufficient- 
ly well. The steam should issue freely through the vent for some time 
before the reading is taken. 
A word or two, now, on the mode of applying the following table 
to the calculation of the height required. . 
1. When the thermometer has been boiled at the foot and at the 
summit of a mountain, nothing more is necessary than to deduct the 
number in the column of feet opposite the boiling point below, from 
the same of the boiling point above:—this gives an approximate 
height, to be multiplied by the number opposite the mean temperature 
of the air in Table II. for the correct altitude. 
feet. 
) 
Example. Boiling point at upper station ........ 201.5 = 5600 
Ditto at lower station ........ 211.3 = 350 
Approximate height, 5250 
Temperature of air, above, 35° 
below, 50 
Meani42,0 —"multiplier,.... sieeiss ecae= IeOee 
Correct altitude, ........ft. 5365.5 
2. When the boiling point at the upper station alone is observed, and 
for the lower the level of the sea or the register of a distant barometer 
is taken, then the barometrical reading had better be converted into 
feet by the usual method of substracting its logarithm from 1,47712 
(log. of 30 inches) and multiplying by .0006, as the differences in the co- 
umn of “‘ barometer’’ vary more rapidly than thosein the ‘‘feet’’ column. 
