Observations zuitli Barojiieters and TJicniiouieters. 173 



It may be mentioned that of eighty-one obsei'\'ations in all, 

 thirty were taken with Yan Yean water, and the rest with rain 

 water, but no perceptable difference in pressure was indicated 

 from the alteration. 



So far as they go the observations tend to show that pressures 

 determined from boiling points are fairly trustworthy. It 

 remains to be seen, however, how much the index error of the 

 thermometer will vary with time, and this can only be done by 

 repeating the experiments after the lapse of some years. Further 

 the writer has not had the opportunity of applying the method at 

 considerable altitudes, though determinations of the height of 

 Arthur's Seat made by him with boiling thermometers were 

 fairly satisfactory, four determinations giving 1016 feet, 981 feet 

 and 986 feet respectively, as against 996 feet determined by spirit 

 levelling. The first three observations were taken with ther- 

 mometers nmch less sensitive than that described above. The 

 aneroid barometers gave the following heights for the same 

 mountain. Watkin (two observations) 1057 feet and 1082 feet. 

 The 2Jr inch (two observations) 961 feet and 1042 feet ; and the 

 If inch (one observ^ation) 927 feet. 



Boiling-point thermometers are condemned emphatically by 

 Mr. Whymper as the result of his experiments on the Andes, 

 but the apparatus used l^y him seenjs to be much less sensitive 

 than that used by the writer. Boiling-point thermometers 

 are generally graduated from about 180 degs. to 212 degs., 

 and are about 12 inches long, the bulbs are placed close 

 to the water of which the supj^ly is very limited, and the 

 heating arrangements appear to be of a meagre character. In 

 some experiments made by the writer with a Greiner Boiling- 

 Point apparatus, constructed about i860, and filled with water 

 so as to just touch the bottom of the bulb, the water had all 

 boiled away before the " pumping " action of the thermometer 

 had ceased. Mr. Whymper's experiments were made with 

 Henderson's apparatus, in which the heating agent is a composi- 

 tion candle. The writer has not used this apparatus, but 

 questions its ability to give a full supply of steam at a high 

 altitude. 



