80 The Total Solar Eclipse of 1900. 
result proved that the freedom thus obtained from anxiety with regard to a 
delicate adjustment, in the excitement of mid-totality, was a most substantial 
gain. 
Asa check on the adjustment of the instrument, a small collimator was attached 
rigidly to the camera, with its object-glass placed immediately above the prism. 
Behind the eye-piece of this telescope was placed a card, with two cross-lines 
marked upon it. This telescope was fed with light from the 12-inch mirror, 
which also supplied the camera itself, and it was adjusted so that when the Sun’s 
image was placed centrally on the cross-lines of the collimator, the spectrum fell 
upon the middle of the exposed photographic plate. If from any cause, either 
from an accidental jar, or in consequence of the diurnal motion, the spectrum 
became displaced upon the plate, it was possible by this device to bring it back 
at once to its proper position by a readjustment of the mirror. In this way the 
spectrum was suitably placed a few seconds before the total phase began; but 
during totality the displacement was not of sufficient importance to necessitate a 
readjustment of the mirror. 
Sir Howard Grubb took charge of the exposure-cap and the flat mirror and, as 
the total phase approached, stood ready to readjust the latter, should the finder 
show it to be necessary to do so. At the same time, I stood grasping the handle, 
and ready to commence turning it when I thought the proper moment had arrived. 
We had intended to commence exposing plates 5 secs. before the beginning of 
totality, as nearly as possible; but, although the diminishing are of sunlight 
appeared to be still of considerable width when I gave the word to uncap, I was 
surprised to hear, almost immediately afterwards, as it appeared, Dr. Downing’s 
signal that the total phase had begun. The interval appeared to be about 2 secs., 
and certainly the first plate had been exposed before Dr. Dewning, who was 
observing with a celluloid grating in one tube of a field-glass, saw the flash-lines, 
and gave the signal. 
The exposures were continued without intermission till 15 secs. after the 
second contact, commencing with a duration of 1 sec., and gradually increasing 
in length, until at the end they occupied rather more than 2 secs. 
When the whole twelve plates had been exposed, our business was to close 
the slides, to remove the two carriers, to replace them by a similar pair contain- 
ing fresh plates, and to withdraw the slides of those in readiness for the exposures 
to be made before and after the third contact. Unfortunately, at this stage, a 
hitch occurred, one of the slides being overlooked. The changing of these carriers 
occupied us for about 25 to 30 secs., after which we had about half a minute to 
view the eclipse with the naked eye, and by the aid of binoculars. 
At 65 secs. from the beginning of totality the exposure of the second series 
of plates began, at first slowly, giving about three seconds, and gradually 
