I arrived at work on Monday, July 9, 2012, to a discover a post-it message on my desk saying, more or less, “John –* has an old 2.5-inch Ramsden telescope and would like some advice on maintenance and restoration”.

Now, I know nothing about  restoration of old telescopes – I leave that to our team of conservators. But the name Ramsden jumped out at me. Jesse Ramsden lived from 1730 to 1800. He was a skilled and successful scientific instrument maker, making such things as sextants, theodolites and of course telescopes. His greatest contribution was the perfection of the ‘dividing engine’, a rotating table used to accurately, precisely and repeatably inscribe marks on brass circles. Why? These formed the curved scale for measuring angles in the sky (on telescopes) or along the horizon (on theodolites). It might not be something you’ve thought of before but producing an accurate protractor from scratch, which is essentially what he did, is not simple. There is a close copy of Ramsden’s dividing engine, made by the equally famous John Troughton, at London’s Science Museum. Nearby is Ramsden’s Great Theodolite, looking like something out  of a steampunk workshop!

Amateur astronomers would know the name Ramsden from the old style of eyepiece that used to be supplied with small telescopes.

The 'Ramsden' inscription on John's telescope. Note the 'Je' inscribed within the 'R'. Photo Andrew Jacob © Powerhouse Museum, Sydney.

So, to John’s telescope. It probably wasn’t made by Ramsden himself, after all he had a workshop with 60 staff, but it is inscribed with his name. It is a little scratched and has a few small dents and the altitude rack (on the diagonal rod in the top picture) is damaged. It moves without slack in both azimuth and altitude and the focus mechanism is firm and positive.

The objective is in excellent condition and there were two eyepieces so I wondered what the view was like. We set it up on a table and looked across Sydney Harbour to the building-tops of North Sydney. Everything was crisp and clear almost to the edge of field – only minor defocus was visible near the very edge. There was no distortion visible at all, even when gently scanning the tube back and forth. The objective glass had a green tint, and I’m sure the optics were not ‘fully-coated’ like modern telescopes, so the view was slightly darkened. Still, I was very impressed for a telescope made probably before the first fleet dropped anchor in Sydney cove!

John's telescope has been repaired at least once before. As this receipt from 1864 shows the brass pin for the altitude mechanism is 'new'. Photo Andrew Jacob © Powerhouse Museum, Sydney.

The provenance of the telescope is unknown. While I suggested the Observatory would be most happy to permanently care for and preserve it for him, John explained it was a family heirloom passed down from his father-in-law, a British Vice-Admiral. Before that is a mystery.

After John left I did a bit of sophisticated research (i.e. searched the ‘net!) and found an almost identical instrument at the University of Arizona College of Optical Science online collection. So John appears to have himself a circa-1785 Jesse Ramsden ‘Library’ telescope, possibly in its original case. I am very jealous!

* John asked me not to reveal his full name.