68 The Total Solar Eclipse of 1900. 
by the Royal Society and the Royal Astronomical Society. The long wooden 
camera was mounted on wooden supports, and was covered with dark American 
cloth turned inside out. Some trouble was experienced owing to dust being 
blown into the clock-work, and to an instability in the adjustments, due appa- 
rently to warping of the apparatus in the strong sun. After a little experience it 
was easy to make the slight adjustment required to keep the image fixed for a 
considerable time, and the adjustment seems to have been good during the 
exposure of the plates. 
Two photographs of the corona were taken on Sandell’s triple-coated plates, 
and they were developed by Mr. McGoogan, photographer to the Dublin Science 
and Art Museum, who also prepared the transparencies deposited in the rooms 
of the Royal Dublin Society and of the Royal Irish Academy. 
The first plate received an exposure of 50 secs., and the second an exposure 
of about 15 secs. Owing to the actual duration of totality being shorter than that 
predicted, I saw the returning burst of sunlight before the camera was closed 
alter the second exposure. The strong light has caused a reversal on one portion 
of the plate. Both negatives exhibit a faint secondary image, due to reflection 
from the lens. This image was clearly visible on the ground focussing-glass 
when the image of the sun was cast upon it. I am much indebted to Mr. W. H. 
Wesley, Assistant-Secretary of the Royal Astronomical Society, for his great 
kindness in writing the annexed description of the negatives. Mr. Wesley is 
well known as one of the greatest authorities on photographs of the corona. 
Description of Photographs of the Corona. 
(By Mr. WESLEY.) 
Plate A (50 secs. exposure). This plate shows a coronal extension of more 
than a lunar diameter in the north-west, of about a diameter on the east side, and 
of more than a diameter in the south polar region; in the north the extension is 
a little less. The prominences are well defined, showing the focus to have been 
good, but there is a certain haziness about the photograph generally, rendering 
the details somewhat indistinct; this is especially shown in the fine rays fillmg 
the north polar rift, which are very ill-defined as compared with Plate B. The 
sky is a little fogged, as was to be expected with so long an exposure. 
Plate B (15 secs. exposure). The coronal extension is about three-fourths of 
a diameter on the west, about half a diameter on the east, and more than one- 
third diameter in the polar regions. The extension is thus less than in Plate 1, 
but the definition is much finer, and the corona close to the limb appears quite 
as dense as in the other plate. ‘The fine rays which fill the north polar rift are 
