572 
MR. J. NORMAN LOCKTER ON THE 
plates were backed with pitch dissolved in benzene during the night preceding the 
eclipse ; the remaining twelve were left untouched, and do not appear to have suffered 
in any way from the effects of halation. 
Exposure of the Plates. 
All the operations for exposing the plates were performed by myself, durations 
being allowed according to a table drawn up by Professor Lockyer. The plates 
were successively brought into position with the rack and pinion of the dark slide, 
and the length of exposure was regulated by means of the shutter in front of the 
prisms. 
About the beginning and end of totality the exposures were short, whilst at mid¬ 
eclipse the longest duration was given, followed by one of instantaneous exposure. 
Also at successive intervals similar exposures were made, as shown by the appended 
tables :— 
No. 
Exposures. 
No. 
5 
Instantaneous 
9 
6 
5 seconds 
10 
7 
30 „ 
11 
No. 
Exposures. 
No. 
6 
5 seconds 
15 
7 
30 „ 
16 
8 
15 „ 
17 
9 
Instantaneous 
18 
10 
5 seconds 
19 
Thus not only are individual plates comparable, by a reason of like exposures, but 
also a series of them. 
The Plates Obtained. 
A list of the photographs taken is given in the accompanying table. The first 
column gives the numbers of the photographs for use in subsequent references, and 
indicates also the order in which the photographs were taken. The second column 
indicates the kind of photographic plate, while the third column indicates the amount 
of exposure, as reckoned by a watch; “instantaneous ” means that the shutter was 
opened and closed again as quickly as possible. The intervals elapsing between the 
exposures of successive plates are shown in Column 4. These could not be reckoned 
directly by the watch, but from previous experience and the summation of times of 
exposure deducted from the total duration they were indirectly estimated. When 
taken in conjunction with the lengths of exposure, the intervals enable us to form an 
estimate of the interval from the beginning or end of totality at which any one of the 
plates was taken. This method of recording the times was adopted because no time¬ 
keeper was available. Photograph No. 2 was probably taken within two seconds 
after the commencement of totality, while the end of totality took place between the 
exposure of Photographs Nos. 18 and 19. 
