Page:Proceedings of the Royal Society of London Vol 69.djvu/260

244 " Abney " squares were printed on No. 6 when the plates were put in their carriers the night before the eclipse. The exposure given was 15 s to the light of a standard candle at the distance of 5 feet.

Of the eight photographs taken, the two by Burckhalter's method of an occulting shutter, are failures. The failure is not due to any fault in the method, but apparently is entirely owing to insufficient expo- sure, the corona photographed on the plates not extending as far as had been anticipated from previous eclipses. It seems probable that with a clearer sky these would have been quite satisfactory.

The other six photographs are excellent. The programme of expo- sures, which was carefully arranged with the Astronomer Royal before leaving England, has resulted in a well graduated series of photographs from No. 1, which shows the prominences and a small amount of corona to No. 5 in which the extension is shown to about 25' from the Moon's limb. The polar plumes and the coronal streamers are well brought out, as well as the remarkable detail of the inner corona. Two features call for special note: (1) the polar streamers round the Sun's north pole are not nearly so extensive as those round its south pole ; (2) a very remarkable arch in the corona round the large prominence at position angle 145 (measuring N.E.S.W.). Round this prominence three separate arches are shown, one inside the other, their radii being 1',2'.4, and 3'.7 respectively. They have the appearance of layers of clouds over an eruption.

(2.) Small-scale Photographs to show Extension of the Corona. The double camera was used in this eclipse exactly as at Ovar to carry a Dallmeyer rapid rectilinear lens of 4 inches aperture and 34 inches focus working at f/8 (lent by the Royal Astronomical Society), and a " Unar " lens, by Ross, of 2'4 inches aperture and 12 inches focus, working at//5.

Eight plate-holders, each taking a pair of 16 cm. x 16 cm. plates, were used during totality. The exposures, to avoid any possibility of shake, were made by holding a cover in front of the object glasses.

The mounting was exactly as at Ovar. i The exposures were as follows :

No. Duration. Plate,

sees.

1 5 Wratten and Wainwright Instantaneous.

2 20 Ilford Empress.

3 10 Imperial Ordinary.

4 35 Imperial Special Rapid.

5 20 Imperial Ordinary.

6 35 Imperial Sovereign.

7 5 Wratten and Wainwright Instantaneous.

8 10 Imperial Ordinary.