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POPULAR SCIENCE REVIEW. 
than that in the cause of science when Europe was in arms from the North 
Cape to Gibraltar and Matapan. France also, when in the throes of a 
terrible revolution, and threatened by armies on all sides, could employ 
Delambre and chain to measure an arc of the meridian, under circum- 
stances of such difficulty and danger that the completion of the task is 
among the wonders of science. Truly our boasted progress is of question- 
able value, if the spirit which has rendered it possible is to be thus 
forgotten. 
The Sun's Corona . — The subject of the sun’s corona has attracted a con- 
siderable share of attention among astronomers of late. The progress of 
discussion thus far has not been without effect, Mr. Lockyer having with- 
drawn his support from the theory that the corona is due simply to the 
passage of the direct solar rays through our atmosphere. He has now 
reverted to La Hire’s theory that a possible action at the moon’s limb may be 
in question. Mr. Seabroke has drawn up a defence of the original form of 
the theory in a paper on “ The Determination whether the Corona is a Solar 
or Terrestrial Phenomenon.” He takes the case of a point on the earth 11 where 
the limbs of the sun and moon are in line ; that is, where the eclipse is total, 
exactly,” and proves in a sufficiently satisfactory manner that under these 
circumstances the spectrum seen by Col. Tennant might be accounted for, 
as also the different spectra seen by the American observers. Only one 
thing seems needed to make the demonstration complete ; namely, that the 
Indian and American eclipses should have been “total, exactly.” As they 
were in reality very far from being only exactly total, and as all the con- 
ditions of the problem are thus completely modified, it would scarcely seem 
that Mr. Seabroke’s demonstration is to be regarded as complete. It may 
be remarked, however, that even if it were, it would only demonstrate the 
possibility that the spectroscopic observations can be accounted for in one 
particular way, by no means that they cannot be accounted for in any other 
way. As a matter of fact, it seems abundantly clear that the spectroscopic 
evidence, like all the direct evidence hitherto adduced, flatly contradicts the 
theory that the corona is a terrestrial phenomenon ; but even if it did not, 
it could not establish that theory. 
Orbit of a Centauri . — The star a Centauri is perhaps the most remarkable 
double star in the heavens. The apparent path in which the companion 
moves is very nearly a straight line, owing to the plane of the orbit being 
nearly directed towards us. The determination of the real path pursued by 
the smaller star around the larger is not therefore rendered impossible, but 
the problem becomes exceedingly difficult. The results obtained hitherto 
have not shown a very satisfactory agreement. Thus Captain Jacob makes 
the longitude of the ascending node of the orbit 8G° 7', the distance of the 
perihelion from the node 291° 22'; the inclination 47° 5G', and the period 
77 years. Hind makes these quantities respectively 17° 22', 26° 2', 62° 53', 
and 81 '40 years. Mr. E. B. Powell had made the longitude of the ascend- 
ing node 177° 50', the inclination 77° 50', and the period 75 , 30 years. He 
has lately obtained fresh data for solving the problem. He remarks that 
u had invited attention in 1804 to the important part of the orbit about 
to be described, viz. the extremity of the perspective ellipse corresponding to 
the lesser maximum of distance.” " I have now to state,” he proceeds, “ that 
