Astronomy. 77 



force at the Earth are considered, both generated by the Sun, 

 one of which may be called the radiant field and the other the 

 coronal field. The radiant field is propagated in rectilinear lines, 

 and has been ordinarily discussed as phenomena of the aether, 

 called heat and light ; hence its direction towards the Earth is in 

 the plane of the ecliptic. A sympathetic study of the electro- 

 magnetic theory of light, and the recent discoveries in electrical 

 oscillations, naturally leads one to a belief in this view, which is 

 here assumed. The coronal field has been shown by the author 

 to be formed by the same forces that are exhibited in the Solar 

 Corona, of which it is the invisible extension ; hence, the second 

 premise is that the coronal field is directed perpendicularly to the 

 ecliptic in the neighborhood of the Earth. It may be shown that 

 the relative intensities of these two fields can be discovered by a 

 consideration of the observed movements of the magnetic needle. 



The solution of the problem depends upon ascertaining the 

 mutual action, at any station, of the distribution of magnetism re- 

 ferred to three poles, the permanent pole, the rotation pole, and 

 the translation pole, the names being assigned from important 

 characteristics. These poles change their relations in diurnal, 

 annual, and secular periods, depending upon known astronomical 

 laws; thus the permanent pole, or the pole of the permanent mag- 

 netism of the Earth in the same hemisphere as the station, wan- 

 ders in a secular period of long duration in the Earth's crust, and 

 also rotates daily about the Earth's axis. The rotation pole, or 

 the pole of induced magnetism, resulting from the earth's rotation, 

 is an instantaneous pole formed successively by induction, its 

 direction being a few degrees from the Sun, and lying near the 

 plane of the ecliptic. The translation pole, or the pole of mag- 

 netic induction, formed by the motion of the Earth in its orbit, 

 lies nearly along the line of the orbit as it pierces the Earth, and is 

 also instantaneous. 



After a discussion of the mathematical analysis required to 

 solve the problem, particularly as to the position of the three 

 poles, the composition of the fields, etc., the author goes on to 

 say that a complete study of this problem will lead to the forma- 

 tion of equations of condition from observations, which, when 

 solved, will give completely the unknown quantities, namely, the 

 constants employed and the forces of the two cosmical fields. 

 These being obtained, we can return to the problems of solar 

 physics with renewed data. Hence, the magnetic needle on the 

 earth's surface will probably be added to the spectroscope, the 

 polariscope, and the bolometer, as an instrument for studying the 

 constitution of the sun. 



Some conclusions drawn are thus stated : Long periods. — 

 The variations of the intensity of action in the sun cause 

 corresponding fluctuations in the fields of force, detected as 

 the 56-year, the 11-year, or other periods; if sporadic, as ter- 

 restrial magnetic storms. Since the poles of the corona do not 

 coincide with the axis of rotation of the sun, the coronal field of 



