20 THE AIR 



rection is required ; in the last case, unless it is known 

 that rain fell, the contents could be treated as all due 

 to spray, and thrown away unrecorded ; but if the 

 water is slightly salt, a note must be made of the fact, 

 and the measurement entered with a query. Much 

 valuable information could be obtained, even without 

 a rain-gauge, if the time when rain began and ceased 

 were recorded in the log, with a descriptive note as 

 to whether the fall was light, heavy, or torrential. 

 It is surprising that so few ships' officers have thought 

 of recording this almost unknown factor of sea climate. 



The Upper Atmosphere. 



Until quite recently we had no practical means of 

 taking observations in the upper regions of the 

 atmosphere, but of late many experiments have been 

 made, by means of kites and balloons, which give 

 excellent results ; and the upper atmospheric regions 

 are being gradually explored and systematically 

 studied. Recent research on the temperature and 

 other conditions in the free air at great heights have 

 shown that normally the temperature falls rapidly as 

 the height increases, until an elevation of six miles 

 (more or less) is reached, where the temperature is 

 from 30 to 70 below zero Fahrenheit, after which there 

 is practically no further decrease of temperature, but 

 sometimes a distinct increase. The upper region of 

 nearly uniform temperature has been termed by 

 physicists the " isothermal layer," or, less aptly still, 

 the " isothermal column." It might be better named 

 (in conformity with the nomenclature recognized by 

 ocean ographers for the depths) the homothermie 

 region. No vessel specially equipped for oceano- 

 graphical research should be without a supply of 



