1891.] on Recent Total Solar Eclipses. 275 



intensity of moonliglit, while Langley found that at a distance of 

 three minutes the corona radiated with one-tenth the intrinsic 

 brightness of the moon. 



Considering (1), that the brightness of the corona diminishes 

 with the distance from the sun's limb ; (2), that Langley observed 

 at the top of Pike's Peak, at an elevation of 14,000 feet in a very dry 

 atmosphere, while Thorpe's observations were taken at sea-level under 

 unfavourable circumstances ; also (3), that the type of corona was 

 diiferent on the two occasions ; the results agree to a remarkable 

 degree, and show that the eye estimates which have suggested 

 enormous differences in the brilliancy of the corona in different 

 eclipses are not to be trusted. 



Returning to the four alternatives respecting the constitution of 

 the corona, we may at once reject the first and fourth ; for it may be 

 proved that the sun could have no regular atmosphere to the extent 

 indicated by the outlines of the corona, and spectroscopic results 

 exclude the hypothesis that the bulk of its matter revolves with 

 planetary velocity ; though probably there is some meteoric material 

 which does revolve round the sun. 



Dr. Huggins, in a lecture delivered in the Royal Institution,* 

 has suggested a theory of the corona, according to which its 

 luminosity is due to electrical discharges, the matter conveying the 

 discharge being projected from the sun by electrical repulsion. The 

 author agrees with Dr. Huggins in the idea that electrical discharges 

 are probably the cause of the streamers which form the most 

 prominent feature of the solar corona. But before we can form any 

 definite ideas as to the precise way in which these discharges are 

 brought about, we must first settle the very important question 

 whether the planetary space contains sufficient matter to be a 

 conductor of electricity. Our present knowledge regarding electrical 

 discharges entitles us to say that a body which is at the high 

 temperature of the sun, surrounded by gaseous matter, cannot keep 

 any appreciable charge of electricity, and we have some evidence for 

 saying that once a discharge is set up in interplanetary space there 

 is sufficient matter present to convey the discharge, so that the 

 lecturer feels bound to believe in a direct electric connection between 

 the sun and the planets. If then, as is probable, electric discharges 

 take place near the sun, there must be some cause which keeps up 

 the difference in electrical potential between the sun and outside 

 space. The form of the corona suggests a further hypothesis, which, 

 extravagant as it may appear at present, may yet prove to be true. 

 Is the sun a magnet ? We know that a body at such a high tem- 

 perature cannot be magnetisable, but may not a revolving body act 

 like a magnet, and may not the earth's magnetism be similarly due to 

 the earth's revolution about its axis ? It can be shown that although 

 a revolving body may act like a magnet sufficiently to account for 



* ' Proceedings,' Royal Institution, 1885. 



