Astronomical Transit Telescope

I am trying to locate info on and the locations of Troughton & Simms astronomical transit telescopes made in the second quarter of the 19th century.  The one illustrated here  was used in Halifax, Nova Scotia to rate marine chronometers.  It’s history is known from ca. 1875 but it probably dates to 1826 though a direct link for the transfer of one owner to another is missing, though one may be reasonably surmised and argued.

This instrument is not signed but has the exact dimensions of and characteristics of a T&S instrument advertised (though not illustrated) in their 1834 catalogue.  Specifically, the objective is 2 1/4″ with a 30″ f/l.  The workmanship is of high quality and the details of the knurled knobs, the screw thread profiles and the TPIs of several of the precision screws are shared with T&S instruments.  The screws are pre-Whitworth standard screw threads and are, more significantly, very close to those I have previous studied on T&S astronomical instruments.  The larger screws are marked to indicate with which holes/nuts they were to mate which was common practice at that time.   T&S made both portable and fixed pier bases; this is the fixed base style.  The cost quoted in the 1834 T&S catalogue was £42 0s 0d or, for the improved version, £47 5s 0d.

Marsters astronomical transit?

A transit telescope believed to possibly be the one purchased
by R.U. Marsters.  It is unsigned but has many details and features of
Troughton & Simms transit instruments of the period, i.e. ca. 1826.

I’ve been keeping my eyes open for a similar instrument in both published literature and museums for 30 years and have not found one.  Was it perhaps a very early trial instrument from T&S and hence not signed?  Later and slightly larger T&S astronomical transits were similar — certainly much closer in their details than those by T&S’s contemporaries.

I would very much appreciate receiving info on the locations of very similar astronomical transits or illustrations especially if known to date to the second Q, 19th c.  The key defining larger features are the shapes of the cross axis and the cast iron base.   Please respond via the editor’s address provided in this post.

Additional images of details:

The cross axis and tube junction with striding level in place:

Transit Telescope detail 2

 

The altitude scale and vernier are silver and the lens to focus the lamp on the mirror to illuminate the fiducials is seen in the centre of the axis:

 

Transit telescope detail 3

 

Oil lamp to illuminate the cross hairs.  The light is reflected off a small mirror suspended in the centre of the telescope tube.  It may be removed by unscrewing the small knob seen at the intersection of the tube and cross axis in the image above.  The lamp was, of course, also used to illuminate the declination scale:

Transit telescope detail 4

Transit telescope detail 4

1 reply
  1. Daniel
    Daniel says:

    Great pictures. Thanks for mentioning the precision screws. It is quite hard to find the name of these precision screws! But luckily you also mentioned the precision screws in detail!

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