Related Object Info
2-foot Gregorian reflecting telescope with split object glass micrometer
This brass Gregorian reflecting telescope was the 54th telescope that James Short made with a focal length of 24 inches out of a total 1279 telescopes to date.
The two-foot brass tube has a finder scope mounted at the eye-piece end. The proper left side of the barrel there is a silver plaque engraved with the quartered arms of the Pepperrell and Sparhawk families.
The optical assembly is attached to an altazimuth mount on a pedestal with three folding scroll legs. There are ivory handls on the azimuth and altitude adjustment keys. The altitude key is removable. The adjustment screws for the focusing mechanism and the locking screws have knurled heads.
The primary and secondary mirrors are present. The primary is cracked. A spare secondary mirror is stored in a tin box (see 0002b).
The telescope comes with a split object glass micrometer (also known as a heliometer). It was likely made by John Dollond (I) or Peter Dollond. It is unsigned. The brass frame holds the objective, which is split into two semicircles. A rack and pinion mechanism operates the micrometer by moving the two glasses in opposite directions along a common diameter. The separation is measured on a scale of 0-5.9, with divisions every .05, and a vernier scale of 0-25 gives readings to .01.
There are two brass keys attached to long wooden handles. When fully extended, these are 70.5 cm and 70.8 cm long. The long handles enable the user to adjust the micrometer while his eye is at the eye piece at the other end of the telescope. One causes the split object glasses to move with respect to each other. The other handle and key rotates the micrometer optical system around the axis of the tube.