Page:A Voyage in Space (1913).djvu/261

Rh [At this signal the picture of the round Sun on the screen, over which the dark Moon had been slowly creeping, was covered entirely up, while a representation of the corona was flashed out by means of a mechanical device in the slide. A few more lamps were lowered to represent the comparatively sudden decrease of daylight as totality comes on.

The time-caller counted seconds: one, two, three ... in an even tone up to the 100 seconds agreed upon; the astronomer received the plate-holders (which were imitated in wood and cardboard), put them into the camera, called for an exposure of the required length and its close