78 
SCIENTIFIC SUMMARY. 
ASTRONOMY. 
y HIE Eclipse Expeditions . — The arrangements made by the various eclipse 
parties will be found among the articles. When these lines are read the 
results of the observations will be known to the world. We shall probably 
have learned much as to the nature of the corona, while the doubts which 
have been urged as to its position will (it may fairly be hoped) have been 
finally removed. 
The Zodiacal Eight . — Closely associated with the subject of the corona, 
the zodiacal light has received of late a considerable degree of attention. In 
a long paper on the subject in the Monthly Notices of the Royal Astro- 
nomical Society, Mr. Proctor discusses the various theories which have been 
propounded respecting this object. He remarks that the geometrical con- 
siderations applicable to the zodiacal light are too definite to admit of 
question — in other words, the path to be followed in seeking for a theory of 
the object is unmistakable ; but he considers that hitherto this path has not 
been traced out far enough, 11 the perplexities which presently surround us 
as we follow it having seemed, perhaps, to render further research hopeless.” 
The very difficulties of the subject, however, tend to render the rejection of 
erroneous theories more certain, and therefore must cause the true theory to 
admit of the more satisfactory demonstration. He then proceeds to discuss 
the several theories. He points out first that the rising and setting of the 
zodiacal light, in a manner precisely corresponding with what would be 
observed if it were a distant object like a planet or star, at once disposes of 
the theory that the light comes from matter lying within the limits of the 
earth’s atmosphere. Such matter might seem, on a given occasion, to rise or 
set according to such a law, precisely as a balloon might seem to follow the 
motion of the setting sun : but only by a singular accident, and not syste- 
matically. Again, the theory that the light is due to a ring of matter sur- 
rounding the earth is disposed of by the fact that the gleam shows no 
appreciable parallactic displacement, as seen from difteient parts of the 
earth. Such a ring, if far otf, would form always an all but complete arc of 
light, from the eastern to the western horizon ; The shadow of the moon 
only appearing as a relatively narrow dark rift across the brightest part of 
the gleam. And if the ring were close by, it would be invisible in mode- 
rately high latitudes. Passing to cosmical theories, Mr. Proctor shows that 
the zodiacal light cannot be due to the existence of a disc of bodies, travel- 
