LOW BOILING POINTS OF WATER. 457 



of water, for which purpose a regular set of tables has 

 been computed, * by the help of which and some simple 

 arithmetical calculations, the approximate height at which 

 the observer then stands above mean sea-level is at 

 once indicated. The results however are not altogether 

 reliable, as different thermometers will be found to 

 vary considerably when their boiling points are tried 

 against each other at the same time and place, as also 

 will their indications of atmospheric temperatures. This 

 however involves a number of technical considerations, 

 which are outside the limits of our present purpose : 

 \ve shall therefore merely say that at 18,000 or 19,000 

 feet above sea-level, the boiling point is so materially 

 reduced f that the finger can be plunged into boiling 

 water without scalding it, and the difficulties in cooking 

 things of course become greatly increased. The report 

 of the Expedition to Yarkand for instance, states that 

 " our servants found it impossible to cook pulse, and 

 tea required to be actually boiled for some time, 

 instead of being only infused." The same fact has 

 been frequently noticed by travellers in different parts 

 of the world, while crossing high mountains, and the 

 thing becomes a matter of serious moment, when 

 one is accompanied by a lot of native servants, 

 who live almost exclusively on rice and things 



* See " Tables " for the determination of heights by the temperaturl 

 of boiling water etc. in Hints to Travellers, Edited for the Counci 

 of the Royal Geographical Society 5th Edition revised to 1883, pp. 

 181 to 185' 



f At 19,300 feet water will boil at about 177 Fahr., and a further 

 ascent of about 585 feet will at this great elevation cause the boiling 

 point to fall one degree lower. 



^ Lahore to Yarkand, Account of the Rotite as traversed by the Ex- 

 pedition under Sir T. Douglas Forsyth, by Geo. Henderson, Medical 

 Officer to the Expedition, and Allan O. Hume, F.Z.S., 1873, p. 76. 



