328 
cloth, if used alone for the sides and roof, is objectionable, 
owing to the possibility of wind tearing it away from the 
nails. 
The importance of each photographic party being pro- 
vided with a tent of the kind named cannot be too 
strongly urged. Residents in India will of course have 
no difficulty, but observers from England should prepare 
a tent at the nearest town to the place of observation, or, 
better still, take one with them. To unpack and erect our 
observatory and dark room required about a day, and to 
dismantle and repack it about three hours. To adjust 
and arrange the instruments will require about another 
day, and about two hours for the dismantling and packing. 
Much of our success at Syracuse depended on our being 
provided as described. The entire cost of the building, 
including waterproof cloth, yellow calico, and the fittings 
of the dark room was less than ten pounds. In the erec- 
tion of a temporary construction of this kind, the shelter 
of a wall or building should be sought. 
As these hints are for the practised photographer, and 
not for the tyro in the art, very little need be said about 
the process to be used. No dry process with which I am 
acquainted is adapted for the purpose. It may be sug- 
gested that the old Zosétive process on glass would give 
good results, and I see no objection to using the negative 
process as well. Supposing six plates to be used, three of 
them could be developed as positives, and three as nega- 
tives, the exposures being timed to suit either. Thenega- 
tives taken at Syracuse were not strengthened or intensi- 
fied, and although they were developed as negatives they 
are almost as valuable as positives, as the detail is of so 
delicate a kind that very little of the outer corona can be } 
seen when viewed by transmitted light. As positives, and 
viewed by reflected light, this detail is seen very perfectly. 
There is, however, detail of ancther kind in these nega- 
tives which can only be seen by transmitted light. The 
advantage of the positive process is that the picture is 
chiefly on the surface, but at those parts where the light 
has been most active, the detail would probably be visible 
when viewed as negatives by transmitted light. 
The size of the camera will be determined by the dimen- 
sions of the plates to be used. Plates 5 by 44 inches will 
be quite large enough, and the camera will require to be 
slightly larger. The number of dark slides necessary will 
depend on the number of exposures te be made, and this 
again will be determined by the duration of the totality. 
In India, where the totality will be rather over two 
minutes, it will perhaps be better not to attempt more 
than six exposures, therefore six frames will be needed. 
In Australia at least twelve plates could be exposed, the 
totality lasting over feur minutes. The single frames 
used at Syracuse were found to be so handy and con- 
venient to use that I am undecided in my opinion as to 
whether any advantage would be gained by using double 
or sliding frames. This is a matter which must be left to 
the choice of the operator. The frames may be made in 
the ordinary way, but the corners of the carrier or frame 
itself should be fitted with silver wire or glass for the plate 
to rest upon; and as an extra precaution against defects 
likely to arise through some of the plates remaining in 
the frames half an hour, each corner may rest on blotting 
paper. In fixing on six as the number of plates to be 
used, I am assuming that they will all have to be pre- 
pared so as to be ready at the moment of totality; and I 
see no advantage to be gained by keeping an assistant in 
the dark room during that time ; at most he could only 
prepare one plate, and I consider it preferable that every 
plate should be ready for immediate use. The prepara- 
tion of these plates will require twelve minutes at least, 
and it is at this point and after the exposures are made 
that extra assistance would be valuable. 
It was found at Syracuse that four baths of glass for 
the silver solution were sufficient ; they were covered with 
brown paper to protect the plates from light. The dippers 
NATURE 

[ Aug. 24, 1871 
may be of glass, or varnished wood, and it is better to be 
provided with both, in case of accident. The glass should 
be the best patent plate, selected, carefully polished, each 
one being marked with a cross in one corner, and stored 
in plate-boxes with the marks all in one position ; and in 
all the subsequent operations this mark should be to the 
left hand-—the reason for this will be seen presently. 
The image obtained with a camera as described is small, 
and it is therefore undesirable that any part of it should be 
disfigured by position wires. The necessity for using wires 
may be overcome in a very simple manner. Let the ground 
glass focussing screen (which should be of the finest pos- 
sible kind, patent plate glass before it receives its final 
polish) have pencil lines crossed diagonally, and a single 
line horizontally across the centre of the plate. When 
the instrument is adjusted and stationary the image of the 
sun should travel parallel with this line. A plate should 
then be prepared, and a very small diaphragm being used 
in the lens, the instrument should then be moved quickly, 
so that the image of the sun leaves a trace which will 
appear after development. This will give the north point 
of the sun at the time of the eclipse, and serve as a key 
plate for all the pictures taken. The object of marking 
the corners of the plates will now be seen, and every plate 
used must be so held that in every operation the marked 
corner is touched by the forefinger or thumb of the left 
hand ; then there will be no doubt about the orientation of 
all the pictures. 
Up to this point two operators will be sufficient, one to 
attend to the arrangement of the instruments, and who 
ought to have some astronomical knowledge, so as to 
be able to adjust the equatorial stand, and the other. for 
strictly photographic work. Help will of course be re- 
quired in the erection of the observatory and dark room, 
At the time of the eclipse two other assistants will be 
required, one te count seconds from the clock or chro- 
nometer, and the other to hand the plate frames to the 
assistant at the camera, If a clock beating seconds or 
half seconds were used, the assistant at the camera could 
do the counting, but volunteers will readily be found. 
The plan adopted at Syracuse could not I think have 
been improved. Mr. Fryer was at the instrument making 
the exposures, while I was at the other end of the camera 
changing the frames. At the word “ready” Mr. Fryer 
took off the cap and counted the prescribed number 
of seconds. At his signal “ done” the plate was changed, 
and so on through all the exposures. Captain Speight 
handed te me the frames and took them from me after expo- 
sure, thus saving twenty-five seconds of the time. Sapper 
Gardiner counted seconds aloud. At the signal of totality 
given by Mr. Fryer the counting commenced. At the third 
second the first exposure was made, the three seconds 
being allowed to make sure of absolute totality. A table 
of the times for the exposure of each plate had been 
prepared by Mr. Fryer beforehand, and this was kept in 
view so as to avoid the possibility of mistake. The times 
were arranged in the following order :—3, 18, 30, 15,8 (the 
6th plate was exposed in the telescope camera, with three 
or four seconds to spare at theend). In India there will 
be time for the 6th plate to be exposed in the camera. 
On the day before and on the morning of the eclipse all 
the operators should be in their places to practise their 
different parts, as it will require the greatest possible care 
to avoid mistakes. Everything must be done deliberately 
and without the slightest hurry. 
Previously to the last eclipse it had been supposed that 
the light of the Corona possessed very little actinism, and 
I had been strongly advised to give a full exposure. As, 
however, there was some doubt on the subject, it was 
determined to vary the exposures as stated ; and unless 
the light of the Corona is not the same in all eclipses, I 
see no reason for suggesting any alteration in the time 
for exposing the plates to obtain different results, sup- 
| posing the same kind of lens to be used. Allowance must 
