eye-tube

The hours passed with Rolla and Cunora amusing themselves at the "eye-tube."

The Devolutionist and the Emancipatrix Homer Eon Flint 1908

The hours passed with Rolla and Cunora amusing themselves at the "eye-tube."

The Emancipatrix Homer Eon Flint 1908

The telescope being now properly directed, the eye-tube may be slipped in again, and the sun may be kept in the field as before.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

The latter defect may be detected by cutting out three circular cards of suitable size with a small aperture at the centre of each, and inserting one at each end of the eye-tube, and one over the object-glass.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

For observing objects at great elevations the diagonal eye-tube is often convenient.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

Or (if the elastic cord has already been fastened) we may remove the eye-tube and shift the telescope-tube about -- the direction in which the sun lies being roughly known -- until we see the spot of light received down the telescope's axis grow brighter and brighter and finally become a _spot of sun-light_.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

If not, it will be easy to determine towards what part of the object-glass the eye-tube is directed, and to correct the position of the tube accordingly.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

If the object-glass is not quite at right angles to the axis of the tube, or if the eye-tube is at all inclined, a like irradiation will appear when a bright star is in the field.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

With this arrangement (known as the _diagonal eye-piece_) no adjustment of the eye-tube is required.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862

However, for amateurs 'telescopes the more convenient arrangement is the diagonal eye-tube, since it enables the observer to apply any eye-piece he chooses, just as with the simple sliding eye-tube.

Half-hours with the Telescope Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction. 1862