MILLER— SPROUL OBSERVATORY ECLIPSE EXPEDITION. 281 



magnetic field in the region over which the shadow-cone has already passed. 

 It is thus possible to discern effects having a period approaching that of the 

 local eclipse-interval and others having a period approximately that of the 

 encire or terrestrial eclipse-interval. 



(c) The general character of the system causing the solar-eclipse mag- 

 netic variation is the reverse of that causing the daylight portion of the 

 solar-diurnal magnetic variation. The range of the eclipse variation is 

 comparable with that of the lunar-diurnal variation, and, like the latter, the 

 variation usually consists of a double oscillation during its period of de- 

 velopment. 



(d) The range of the apparent effect on the intensity of magnetization 

 of the Earth during the solar-eclipse magnetic variation, is about equal to 

 that found associated with a lo per cent, change in the solar radiation as 

 shown by changes in the solar-constant values. 



(e) The results at the high mountain-station. Corona, Colorado, indicate 

 that the magnetic effects during a solar eclipse may be modified and even 

 intensified by altitude of station, topography and meteorological conditions. 

 In view of the bearing of these results upon the theory of the solar eclipse 

 magnetic variation and possibly upon the theory of other variations of the 

 Earth's magnetic field as well, it will be highly desirable in the planning of 

 future eclipse work to include as many mountain-summit stations as con- 

 veniently possible. — Terrestrial Magnetism, March, 1919, Vol. XXIV., No. i. 



