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Updated: June 9, 2025
This again carries an observation glass fitted with an eye-piece which can be turned in the vertical plane in the same manner as that of the fore-sight. By means of this ingenious sighting device it is possible to ascertain the range and angle of fire very easily and speedily.
A shallow tray was contrived deep enough to hold the speculum, and fitted with screws, so that it could be secured to one end. Next followed the fitting of a properly-constructed eye-piece from a London optician, contrived so that it looked at right angles into a small reflector, which also had to be carefully fixed in the axis of the great speculum.
"I can't make out what you want with this great instrument," I said. "A common pocket lens would do all that you require. Besides, a six-inch objective will not magnify more than two or three diameters." "Two, with the draw-tube closed," replied Thorndyke, "and the low-power eye-piece brings it up to four. Polton made them both for me for examining cheques, bank-notes and other large objects.
I don't know what there was in those few words, but I noticed that for a minute or two after they, were uttered I heard the ticking of the clock-work that moved the telescope as clearly as if we had all been holding our breath, and listening for the music of the spheres. The Young Girl kept her eye closely applied to the eye-piece of the telescope a very long time, it seemed to me.
The sunshine sparkled on the gray-green waters, and followed them in bright coruscations for a short distance into the mouth of the tunnel, the other end of which, diminished by the distance, opened into the daylight like the eye-piece of an inverted telescope.
The convex lens of the eye-piece was carried not by a tube properly so called, but by four rigid fine wires placed at right angles. This arrangement left the focus open in almost every direction. A concave mirror was then placed so that it threw a very condensed image of the sun laterally on the very spot where the image of the advertisement was formed.
They thought that the image of a small circle cannot be distinct, cannot be sharp at the edges, unless the pencil of rays coming from the object in nearly parallel lines, and which enters the eye after having passed through the eye-piece, be sufficiently broad.
For this purpose Newton fashioned a concave mirror from a mixture of copper and tin, a combination which gives a surface with almost the lustre of silver. When the light of a star fell upon the surface, an image of the star was produced in the focus of this mirror, and then this image was examined by a magnifying eye-piece.
We then lost our footing entirely for the floor of the Deutschland slanted sharply toward the front. I was just able to catch hold of the ocular or eye-piece of the periscope. Down in the central the men were hanging on to the hand-wheels of the diving rudder. A few terrible seconds passed thus. We had not yet seized the full significance of this new situation when there came a severe shock.
He had descended a thousand feet, he was estimating, when the black igneous rocks blazed blindingly with a reflected light like that of a thousand suns. Another hundred feet below, down a precipitous slope, was a broad table of rock. He saw it in the instant before he threw one metal-clad arm across the eye-piece of his helmet to shut out the glare.
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