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Updated: May 9, 2025
At last she turned away from the eye-piece, and looked at him with something like a scared expression in her eyes, and said: "It's very wonderful, isn't it, that one should be able to see all that just by looking into a little bit of a hole in a telescope?
A little after half-past eleven that night Miss Auriole was looking wonderingly into the eye-piece of the great Reflector, watching a tiny little patch of mist, somewhat brighter towards one end than the other; like a little wisp of white smoke rising from a very faint spark that was apparently floating across an unfathomable sea of darkness.
In the "Gregorian" form, the focussed rays are, by a second reflection from a small concave mirror, thrown straight back through a central aperture in the larger one, behind which the eye-piece is fixed. The object under examination is thus seen in the natural direction.
It was really an astronomical telescope; but, like many similar instruments, it was also provided with a terrestrial eye-piece, for I had looked through it across the river, and had marvelled at its far-reaching power.
The eye-piece of the observation glass is so made that it can be turned through a vertical plane in proportion as the angle of fire increases in relation to the horizontal. The determination of the distance from the objective and from the corresponding back-sight as well as the observation of the altitude is carried out with the aid of the telemeter.
In the centre of the solid floor, levelled to the utmost perfection, was left a circular pillar supporting the polar axis of an instrument widely differing from our telescopes, especially in the fact that it had no opaque tube connecting the essential lenses which we call the eye-piece and the object-glass, names not applicable to their Martial substitutes.
The turret was crowned with gold. As I opened the door and stepped inside, I saw a large telescope and a few chairs. The observer's chair was upholstered with velvet. It was not a complicated observatory like the worldly ones.... I removed the cap of the great telescope, covering the object-glass, and then uncovered the eye-piece. Follow me."
The large mirror is not mathematically centred in the large tube that contains it, but is placed rather obliquely in it. This slight obliquity causes the images to be formed not in the axis of the tube, but very near its circumference, or outer mouth, we may call it. The observer may therefore look at them there direct, merely by means of an eye-piece.
If the atmosphere is steady, the image, when the eye-piece is pushed in, will be formed of a great number of minute rings of light. If the glass is good, these rings will be round, unbroken, and equally bright.
"There, Tom," said Uncle Richard; "now I think we can sweep the heavens in every direction, and when once we have tried, the mirrors, so as to set them and the eye-piece exact, we can get to work." Tom looked at his uncle in dismay. "Why, you don't mean to say, uncle, that there is more to do after working at it like this?" "Yes, a great deal.
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