338 
NATURE 
[ Fed. 23, 187% 

its diameter would have been overwhelming, and feeling 
that here was a crucial test to apply to a question which 
has so long been debated, but never with such interest 
among the workers as recently, it was with some excite 
ment that I found myself before these two photographs 
some little time ago with two American astronomers or: 
eminence, for the purpose of endeavouring to settle the 
question. Suffice it to say that we came to the conclusion 
that the rifts were not identical, that the two cameras had 
not photographed the same phenomenon, although at first 
there appeared to be sufficient similarity to make the 
matter appear doubtful, and, unfortunately, the photo 
graphs vary so much in size, and the margin of the 
American one is so limited, that it will be scarcely possible 
to make a final comparison until they are brought to a 
common scale, and superposed the one on the other. 1 
do not think it is surprising that rifts should appear in 
both photographs, supposing a non-solar cause were at 
work, for the Corona between the rifts on Mr. Brothers’ 
photograph looks like a very wide ray, 
Assuming then for the present that the photographic 
evidence goes the way of all the other evidence—that in 
short, the solar corona, including all its fantastic boun- 
daries, has been probably reduced from one, two, or three 
solar diameters, to six, eight, or ten minutes,—I care not 
which,*—let us examine some of the details of the various 
observ ‘tions, 
In Professor Watsen’s drawing, the intimate connection 
between the higher and lower levels of the chromosphere 
(including the portions not at present observed by the new 
method), comes out in a very striking way. Mr. Seabroke 
at my request, made careful maps of the positions of th: 
prominences before the totality commenced, and Professo: 
Watson made his drawing of the Corona, independently 
of the positions of the prominences. On the homeward 
journey the map was compared with the sketch, and t«. 
use Professor Roscoe’s words, “On comparing the two 
drawings thus independently made, a most interesting 
series of coincidences presented themselves. Wherever on 
the solar disc a large group of prominences was seen in 
Mr. Seabroke’s map, there a corresponding bulging out 
* I beg here to give the actual words employed by Dr Frankland and myself 
in the communicat on to the Royal Society on the subject. Speaking of the 
chromosphere, it was remarked “* the tenuity of this incandescent atmosphere 
is such that it is extremely improbable that axy extensive atmosphere, such 
as the corona has been imagined to indicate lies outside it "—Proc. R.S , 
Feb. 11, 1869. I never 1mogined that all the Corona was non-solar. Again, 
Proc. R.S., No 116, 1870 discssing the American Eclipse, [ state that the 
chromosphere includes the ‘* radiance” observed in the American Eclipse, of 
which radiance Dr. Gould wrote as follows :— 
** An examination of the beautiful photographs made at Burlington and 
Ottumwa . . . and a comparison of them with my sketches ef the corona, 
have led me to the conviction that the radiance around t! e moon in the pic- 
tures made during totality is not the corona at all, but is actually the image 
of what Lockyer has called the chromosphere. ‘lhis in:eresting fact is 
indicated by many different considerations. !he directions of maximum 
radiance do not coincide with those of the great beams of the corona; they 
remain c stant, while the latter were variavle. There 1s a diameter approxi- 
mately correspording to the solar axis, near the extremities of which the 
radiance upon the photographs 1s a minimum. whereas the cworonal 
beams in these directions were especially marked during a great 
part of the to'al obscuration. The coronal beams stood in no appi- 
rent relation to the protuberances. whereas the aureole seen upon 
the photographs is most marked in their immediate vicmity. . . . . 
Whatever of this aureole is shown upon the phorographs was occulted 
or displayed by the lunar motion, precisely as the protuberances were 
The vanat ons in the form of the corona, on the other hand, did not seein to 
be depencvent in any degree upon the moon's motion. ‘The singular and ele- 
gant strictural indication in the special aggregations of Ight on the eastern 
side may be of high value in guiding to a further knowledge of the chromo- 
sphere. ‘They are manifest in ail the photographs by your parties which | 
have seen, but are especially marked in those of shortest exposure, such as 
the first one at Ottumwa. In some of the later views they may be detected 
on the other side of the sun, though less distinct ; but th= very irregular and 
iagged outline of the chromosphere, as described by Janssen and Lock-er, 
is exhibited in perfection.” 

of the Corona was chronicled 6n Professor Watson’s draw- 
ing, and at the positions where no prominences presented 
themselves, there the bright portions of the corona ex- 
tended to the smalle:t distances from the sun’s limb.” 
We may remark that these coincidences show the ex- 
cessive fidelity of the drawing, and make it one of the 
most valuable of the products of the Expedition. 
On former occasions the Corona has been stated t» 
assume a roughly four-cornered form. This was als» 
observed in Spain last December, and seems at last ex- 
plained by three drawings made by one of the American 
party there. 
At the commencement and end of totality, when the 
moon unequally covered the sun, the photographs have 
recorded an excess of light on the Corona on the side 
where the limbs occur nearest in contact. I am told that 
this effect in one of Lord Lindsay’s photographs is very 
striking ; it is certainly so in one of Mr. Brothers’. In 
the drawings we have a slightly different effect. At the 
commencement of totality, when the western or right hand 
limbs were in contact, we get Fig. 1, at the end of totality the 
appearance recorded was Fig. 2 ; the picture at the middl e 
1 2 3 

of totality compounding both these appearances, and being 
roughly represented by Fig. 3, in which the rectangu.ac 
appearance comes out in its full strength. 
A word now about the polariscopic observations. I 
may remark on this that it is much more easy for us 
to explain slight polarisation which might be atmo- 
spheric, than it is to explain, if we content ourselves with 
laboratory experiments, strong vada/ polarisation which 
must take place at the sun. If we assume that gas or 
vapour of considerable tenuity does not reflect light 
(although I think this is to assume very much for the gas 
or vapour a¢ ¢he sum, at all events), what is it that reflects 
light to us at the sun, and reflects it apparently only 
above the level of the intensely incandescent hydro- 
gen? Certainly not sclar spray. If we deny reflection to 
gases altogether, may it not be the continuous portion 
of the spectrum of the gas itself to which the light is 
due. But this question of polarisation is certainly one 
in which very much remains to be done, and it is conso'ing 
to know that the results obtained now will much facilit we 
the planning of the next polariscopic campaign, which, we 
may add, should not be deferred beyond the end of this 
year. J. NOkKMAN LOCKYER 

PHYSICAL LABORATORIES 
‘ie an excellent article in a late number of NATuRF, 
Prof. Pickering has drawn attention to the importance 
of the practical teaching of Physics, and has shown how 
this is being done on an extensive scale in America. It 
may be interesting to trace the similarity between the 
methods employed by different teachers, and to show what 
opportunities are and have for some time past been open 
to students in London for the practical study of every 
branch of Physics, 
