Observations witJi Barometers and Thcrvwnieters. 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 boihng 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 

 •1 ---i_i„ „uu„,io« tlionoh determinations of the heidit of 



After the word "givino-" on linp 1 •? .^ ito • 



to "Jft on line id, page 173, insert, "1 



016 feet,". 



leveinng. xnc 1.1.^^ .^..^„ . 



mometei's much less sensitive than that described above. The 

 aneroid barometers gave the following heights for the same 

 mountain. Watkin (two observations) 1057 feet and 10S2 feet. 

 The 2i inch (two observations) 9G1 feet and 1042 feet ; and the 

 1-| inch (one observation) 927 feet. 



Boiling-point thermometers are condemned emphatically by 

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

 but the apparatus used by him seems to be much less sensitive 

 than that used by the writer. Boiling-point thermometers 

 are generally graduated from about ISO clegs, to 212 degs., 

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

 to the water of which the supply 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 1860, and tilled 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. 



