DIY History | Transcribe | Scholarship at Iowa | Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no.26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903 | Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no. 26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903, Page 4

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Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no.26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903

Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no. 26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903, Page 4

The instrument is necessarily provided with a diagonal eye-piece for observing transits of stars near the zenith.

                    Alidade or "Setting" Circle
                          and Vernier

In order to facilitate setting the telescope at the right altitude to catch a given star, a small graduated circle is attached to the axis near one end. It turns with the axis while the vernier is kept stationary and shows the angle thru which the telescope is rotated. The vernier is set horizontal by means of an attached spirit level called the alidade level. When the vernier reads zero and is set horizontal the telescope points to the horizon. The arm carrying the vernier is sometimes called the alidade, and the circle is sometimes called the alidade circle, or vertical circle.
      An arm carrying a reading glass is attached to the axis to and in reading the vernier. The reading glass may be moved sideways or up and down.

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The instrument is necessarily provided with a diagonal eye-piece for observing transits of stars near the zenith. Alidade or "Setting" Circle and Vernier In order to facilitate setting the telescope at the right altitude to catch a given star, a small graduated circle is attached to the axis near one end. It turns with the axis while the vernier is kept stationary and shows the angle thru which the telescope is rotated. The vernier is set horizontal by means of an attached spirit level called the alidade level. When the vernier reads zero and is set horizontal the telescope points to the horizon. The arm carrying the vernier is sometimes called the alidade, and the circle is sometimes called the alidade circle, or vertical circle. An arm carrying a reading glass is attached to the axis to and in reading the vernier. The reading glass may be moved sideways or up and down.