Lectures on Practical Astronomy and Astronomical Instruments (1879)
Challis, James Rev. · Deighton, Bell and Co. (Cambridge) · leaf 56
THE TRANSIT INSTRUMENT. 27 of the level may be set to any required graduation-reading. In the figure, cd is the spirit-level of one of the setting-circles, the vernier being attached to the end d. The position of the zero … reading of the setting-circle is so adjusted that when the tele- scope points to the zenith, and the bubble of the spirit-level is in its middle position, the index reading is equal to the co-lati- tude of the Observatory. Hence for any other pointing of the telescope the index-reading for bubble…
Book · Astronomy
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