Page:Proceedings of the Royal Society of London Vol 69.djvu/243

Rh The cameras were focussed on trees on a distant hill viewed through blue glass, and gave satisfactory images.

The programme of exposures was the same as that for the Dallmeyer telephotographic camera, as follows :

8 seconds, 16 seconds, 32 seconds, 120 seconds, 4 seconds, 2 seconds, thus including one long exposure, and five others in geometrical progression, it being intended to compare the polarised image on one plate with the unpolarised image on the plate next before it in the series. The Savart was to be set in accordance with the result of visual observations of the atmospheric .polarisation, so that the bands due to atmospheric polarisation should be obliterated. The first photograph was made with an arbitrary setting of the Savart, and the setting chosen was one that would give the coronal bands slightly inclined to the sun's equator. In the event no atmospheric polarisation was detected, and the Savart was left at the same setting throughout all the exposures. Mr. Wallace made simultaneous exposures for these and for the Dallmeyer telephotographic camera.

Results. As in the case of the Dallmeyer telephotographic camera, four photographs were obtained, standard squares being impressed on each plate after the eclipse with a standard candle at 5 feet.

Exposure for Exposure for standard

corona. squares.

No. 1 8 seconds 10 seconds and 5 seconds

2 17 20 5

,,5 4 20 5

,,6 2 5 (one only).

All the photographs with the Savart camera are good clean plates and show marked polarisation of the corona. The following table summarises the extensions of the coronal streamers in the unpolarised images and of the bands in the polarised.

Extensions expressed in Minutes of Arc from Moon's Limb. P = Polarised Image. U = Unpolarised.

Plate

No. 1.

No. 2.

No. 5.

No. 6.

Exposure

8 seconds.

17 seconds.

4 seconds.

2 seconds.

North polar streamers East equatorial West

U.

P.

U.

P.

U.

P.

U.

P.

8' 13 8 5

? 57'

49

p

20' 46 41 16

28'(?) 69 97

?

15' 29 29 11

10'(?) 28 34

?

8' 15 20

8

? 10' 23