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Noell

Your quadrant would have been at the lower end of the market and probably used mainly for day time sun observations, when an adjustable rising piece becomes irrelevant. However, for difficult twilight shots, when horizon contrast is poor, an increase in brightness too small to be detected by the eye can bring about an increase in contrast and then being able to "see" more of the horizon may be of use. I cannot say whether it makes a practical difference, as my experience of such shots is very small. I leave it to others to comment.

The vernier of your instrument is probably divided to read to only 30 seconds. Collimation error has to be quite gross to make a difference. An error of one degree is easily seen by eye alone. At an altitude of 75 degrees, this would lead to an observation error of only 48 seconds, close to the absolute limit of the instrument's precision. The error is worst at high altitudes, but even at 85 degrees the error introduced is still less than a minute, important certainly for lunar distance observations, but this class of instrument would not be generally have been used to make them.

The adjustable rising piece of higher-end instruments was no doubt expensive to make and would have involved some hand fitting, but even so, it took a long time for the modern vee-and-flat fork arrangement to evolve. By this time most makers were simply making the telescope axis parallel to the frame in the first place and had abandoned the collimation adjustment which is easy to distort and which anyway was probably in most cases ignored.

Bill Morris
Pukenui
New Zealand
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