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POPULAR SCIENCE REVIEW. 
examination the splendid photographs which were obtained at Dodabetta. 
It should be noticed in passing that the photographs, scarcely (if at all) less 
perfect, obtained by Mr. Davis, who at Lord Lindsay’s charge accompanied 
the English expedition, escaped as by a miracle from the tight grip which 
laid hold of everything else obtained by that party,* and were thus avail- 
able for comparison with those of Col. Tennant. Nothing could possibly 
be more convincing than the evidence given by either series separately, and 
by the two series when taken together. The details of the corona in these 
photographs are very numerous, and wonderfully distinct ; all of them can 
he recognised in all the photographs. We cannot wonder that even those who 
had been most opposed to the solar theory of the corona have at last given 
in their adhesion to it. We do not say that all of them have, for that 
would be expecting too much, human nature being as it is. But that any 
of the opponents of that theory should have adopted it, speaks volumes. 
Now Dr. De la Itue, who, it will be remembered, had urged arguments in 
favour of Oudemann's theory, which may be called the lunar theory of 
the corona, admitted, with a candour and frankness which did him infinite 
honour, that the photographs obtained last December demonstrate the solar 
nature of the phenomenon. 
Densities- of Jupiter’s Satellites. — Mr. Proctor has called attention to the 
incorrect values of Jupiter’s satellites which have found their way into our 
text-books of astronomy. These values have led to erroneous assumptions 
as to the condition of these bodies. The following table shows at once the 
incorrect values formerly adopted, and those which Mr. Proctor has cal- 
culated : 
Satellite 
Mass that of Jupiter 
Density that of Earth =1 
Density that of Water =1 
=1 
Text-book value 
i True value 
Text-book value 
True value 
I. 
0-0000173 
0-0202 
0-198 
0114' 
1-148 
II. 
0-0000232 
0-0302 
0-374 
0-171 
2-167 
III. 
0-000088-5 
0-0698 
0.325 
0-396 
1-883 
IV. 
0-0000427 
00393 
0-253 
0-223 
1-468 
It will be seen that the errors are enormous, nor is there any recognisable 
explanation. For the density of the first satellite is given in our text-books 
at about a tenth of its true value, but that of the third at rather more than 
a fifth. One obtains something very like the text-book values, however, 
by supposing all the satellites equal in size to the first, and by reducing the 
thence estimated density to one-tenth of its value. Assuredly, supposing 
this to be the true explanation — or, indeed, whatever may be the true ex- 
planation — the error is a most monstrous one, to be repeated, as it has been, 
from one hand-book of astronomy to another. It may fairly be asked what 
confidence can be placed in such hand-books when blunders like these are 
suffered by their authors to escape detection. 
Orhit of the Double-star Castor . — Mr. Wilson, M.A., of Rugby, enunciates 
fihe somewhat startling theory that the orbit of Castor is hyperbolic, u a form 
* Probably because, being obtained at Lord Lindsay’s expense, there was 
a private claim upon them. The public claim upon the observations of the 
members of the expedition could be ignored, it would seem ; but, fortunately 
for science, Lord Lindsay successfully urged his claim upon his own property. 
