The practical astronomer : comprising illustrations of light and colours, practical descriptions of all kinds of telescopes, the use of the equatorial-transit, circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy (1845)
Dick, Thomas, 1774-1857 · London : Seeley, Burnside, and Seeley · leaf 339
used, the length of theinstrument extends only to the point I. In look-ing through this telescope, the right eye is appliedat the point H, and the observers head is under- 314 THE PRACTICAL ASTRONOMER. stood to be uncovered, or, at least, tightly coveredwith a thin cap. For those who use only the… … view of the instrument, in which the position ofthe speculum may be seen. All the specula whichI fitted up in this form, having been originallyintended for Gregorian reflectors, have holes intheir centres. The eye-piece is therefore directedto a point nearly equi-distant from the hole tothe left…
Astronomy · Astronomical instruments · Telescopes
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