NavList:

Fred and Norm

The three screws are only for attachmenbt, not adjustment in this Admiralty pattern sextant. Collimation was taken care of by making the part accurately and there is no adjustment for collimation. If the screws are loose, tighten them with a force appropriate to their size. Stability and location is ensured by a large boss sitting in a close-fitting counter-bore on the back of the frame. The triangular rising piece has a "rise and fall" adjustment so that more or less of the horizon may be captured by the left hand side of the telescope objective if required. Even relatively slight increases in light intensity can give disproportionate increases in contrast, which is what is required when the contrast between the horizon and the sky is poor.

Brass can certainly work harden and undergo brittle fracture. Next time you twist the head off a brass screw, note the crystaline appearance of the fracture surface.

Bill Morris

Pukenui

New Zealand