Chemical and Physical Notes 1 1 5 



and of those giving the normal gravitational correction for 

 latitude and for height above the sea. ' 



The use of the hypsometer along with the barometer may 

 give valuable results at sea. It may give us a means of 

 divining changes of depths of the ocean, especially in tropical 

 latitudes where, when the sea is calm, all the conditions for 

 such experiments are most favourable. On land, the subject 

 has been taken up with great zeal by Professor Mohn 1 , the 

 distinguished head of the Norwegian Meteorological Service. 

 He has already published a preliminary report, and further 

 reports from him will be expected with interest. In his hands 

 this method will be thoroughly tested in all directions. 



It is not suggested that such observations should be made 

 by the Antarctic Expedition. The margin of O'I47 C. be- 

 tween the normal boiling-point at the poles and at the equator 

 shows that very fine thermometers would be required, and 

 many other refinements are necessary. It is quite evident 

 that the height of the barometer at o C. can be arrived at 

 with the requisite certainty only if the barometer has been 

 hanging for at least a day in a room of uniform temperature. 

 Of course the whole of the working part of the thermometer 

 must be immersed in the steam. Correction for an exposed 

 portion of the mercurial thread of the thermometer is quite 

 inadmissible. The combined use of the barometer and the 

 thermometer has been discussed at this length because it 

 affords an opportunity of arriving at precise ideas of the 

 fundamental principles of both instruments, and of the uses 

 to which each may be legitimately put. 



A legitimate, and at the same time an eminently practical, 

 use of the hypsometer is to replace the mercurial barometer in 

 the determination of the atmospheric pressure, and in the 

 comparison of barometers at distant stations. On all camping 

 excursions it is necessary to have the means of boiling water, 

 and except under stress of circumstances, it is boiled night 

 and morning. Saturated steam is therefore produced in the 

 ordinary day's work ; it is only necessary to provide the means 

 of observing its temperature accurately. 



1 Das Hypsometer als Luftdriickincsser, von H. Mohn. Christiania, 181)9. 



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