2i 4 INTERESTING SCIENTIFIC WORK IN THE ARCTIC 



instruments of great value to him and records of which are of the 

 utmost importance to science. Among these may be noted the 

 Aneroid Barometer, an instrument used for determining the 

 pressure of the atmosphere. If the pressure at sea level is 

 known, this instrument will give a fairly accurate reading of 

 the altitude at which the observer is standing, on the well-known 

 principle that the pressure of the atmosphere grows less in exact 

 proportion as the altitude increases. 



The thermometer, giving the temperature of the air, is natur- 



lly of great interest and value to the 

 .explorer. Several are usually carried, 

 both on account of the risk of accident 

 and because of the great variation in 

 temperature to which they may be 

 subjected. The ordinary mercury in 

 glass thermometer is useless in ex- 

 tremely low temperatures, from the 

 fact that mercury freezes at a tem- 

 perature of 37.8 degrees Fahrenheit 

 below zero. Consequently it is neces- 

 sary to use what are known as spirit 

 thermometers, or instruments in 

 which a fluid having a lower freezing 

 point than mercury is employed. This 



fhiid may be alcohol or a liquid called toluene, known to science as 

 methyl benzene. This fluid is recommended and adopted by the 

 International Bureau of Weights and Measures as giving more 

 accurate results than alcohol. 



If the observer wishes to obtain an automatic record of either 

 the highest or lowest temperature to which the instrument has 

 been exposed, he may use what are known as Maximum or Mini- 

 mum Thermometers. These are simply thermometers contain- 

 ing a device which remains fixed either at the highest or lowest 



ANEROID BAROMETER. 



fwtrument "by Queen & Co., 

 Philadelphia. 



