Page:Proceedings of the Royal Society of London Vol 69.djvu/275

Rh developing the photographs was almost entirely carried out by Mr. Walter and by Mrs. Maunder, to whom the expedition is therefore greatly indebted for the results obtained. The weather being hot and damp, much difficulty was experienced with the different plates tested by way of experiment before the day of the eclipse. Finally the following developer was adopted and found to work well. In spite of its excessive dilution, it was found that fog resulted if its strength was materially increased.

Solution A.

Metol 40 grains.

Hydroquinone 50

Sulphite of soda 120

Bromide potassium 15

Water 20 ounces.

Solution B.

Caustic soda, 100 grains.

Water 20 ounces.

For development half an ounce was taken of each stock solution and made up with water to 30 ounces, 15 drops of a 1 per cent, solution of bromide of potassium being added. During development this solu- tion was strengthened by the gradual addition to it of a solution com- posed of 1 ounce of each of the two stock solutions made up with water to 10 ounces. But the stronger solution was seldom added to the weaker in a greater proportion than 1 to 15. The average time of development was 75 minutes.

Photographs of the Partial Phase. These were taken with the photo- heliograph of the Royal Alfred Observatory, Mauritius, already described. The aperture for this purpose was reduced to 1|- inches, and the exposure given by the drop-slit in the primary focus. Mr. T. F. Claxton made the exposures, and called the times by Kullberg 3400 to Bombardier Cox, who entered them. There being only three plate -carriers available for this work, Mr. C. Garrioch remained in the dark room to change the plates, and Bombardier Truman ran to and fro with them. The plates used were Cadett and Neale's ordinary lantern plates. The times of exposure were as follows :