ELECTRIC DISCHARGES 25 



cirrous clouds. At other times the aurora appears as 

 pulsating waves of white light, flashing across the sky 

 in independent action. An aurora is generally white, 

 but: the display is often accompanied by a decidedly 

 red appearance of the sky. St. Elmo's fire, which 

 appears as a sort of electrical discharge, occurs in the 

 height of storms, not always thunderstorms. These 

 fires indicate a highly electrical state of the atmosphere, 

 the light seeming to play round the mastheads and 

 yards of a ship with a faintly white glow. It would be 

 worth noticing whether the steel masts of a steel ship 

 with wire rigging would show this effect. 



Finally, in all measurements and descriptions the 

 observer is earnestly counselled to regard only what he 

 sees, remembering that the main value of his observa- 

 tions, if they turn out to be of value, lies in the testing 

 of the truth of theories, not in finding what other 

 people have noticed before. It is extremely desirable 

 that anyone aspiring to make observations of value in 

 marine meteorology should consult the instructions 

 issued by the Meteorological Office, study the pilot 

 charts of the parts of the ocean which are published 

 monthly or at more frequent intervals, and consult 

 such standard works as are cited in the List of Litera- 

 ture given on p. 434. 



