Page:Proceedings of the Royal Society of London Vol 69.djvu/274

258 (3.) Photographs on the Q-3-inch Scale.

These were taken by Professor T. A. Pope, of the Koyal College, Mauritius, with a Dallmeyer rapid rectilinear lens of 4 inches aperture, and 32 inches focal length, Mr. E. G. Eowden exposing at the object- glass at the same time as he exposed for the Mauritius photohelio- graph, which was mounted immediately below it. Six plate-carriers were provided for this instrument, and six photographs of the corona were secured.

No.

From

To

Duration of exposure.

Plate.

1 2 3 4 5 6

Bell 3 6 9 12 15 18

Bell 5

, 8, 11 , 14

, if

, 20

sec. 20 20 20 20 20 20

Imperial Process. Ordinary. ,, Special Rapid. Ilford Empress. Wratten and Wainwright Instantaneous. Imperial Fine Grain Ordinary.

The plates used were 16 cm. square, and the Sun was placed a little to the west of the centre of the field, so that Venus and Mercury might be included in the photographs. As they are well shown on all the plates, there was no need for any other mode of orientation, and no special photographs were taken for that purpose. Nor were the " Abney squares " printed on any of the plates with this instrument.

No. 1. A good clear negative. On the west side of the corona four straight rays are seen, the two longest extending about 1^ from the Moon's limb. On the east two chief rays are seen, forming the edges of the great east equatorial wing of the corona. A fainter ray runs nearly parallel to the great N.E. ray. The rays on the E. are traceable to about 1 from the Moon's limb.

No. 2. Neither so dense nor so clear as No. 1, nor can the rays be traced quite so far upon it.

No. 3. The sky glare has come up on this plate, which in con- sequence shows less than Nos. 1 and 2.

No. 4. Definition poor.

No. 5. Definition poor.

No. 6. Very dense image ; the rays on the west can be traced to more than 2 from the Moon's limb.

The Dallmeyer K.R. lens was focussed by repeated photographs of star fields, especially of the field of the Southern Cross.

Development of the Photographs. Owing to my having been taken ill on May 21 with a severe attack of malarial fever, .the work of