Reflecting the past

Earlier this year, we came across some old scientific instruments kicking around Wesleyan’s Exley Science Center: microscopes and preparation plates, spirit levels, laboratory equipment, and, most interesting to us, a couple of small telescopes. What was interesting about this discovery was that several of the instruments dated back to the eighteenth century—a hundred years before Wesleyan was established in 1831.  What were they doing here?

We’ve since been trying to learn more about this collection of (mainly optical) instruments.  Inside their carefully crafted wooden cases, we found a few clues to their identities, if not their provenance.  Typewritten labels, which look to be from the 1970s or 1980s, suggest that these items may have been part of a small exhibit before. Newspaper protecting the more fragile elements dates from the 1960s.  Clearly these devices hadn’t been orphaned for too long—just long enough to be forgotten.

This Gregorian refracting telescope seems to date from the mid-1700s. An old handwritten label indicates that it was probably manufactured by Mann and Ayscough, who worked together from 1743 to 1747.

This Gregorian refracting telescope seems to date from the mid-1700s. An old handwritten label indicates that it was probably manufactured by Mann and Ayscough, who worked together from 1743 to 1747. Van Vleck Observatory collections, Wesleyan University.

The two telescopes in the collection are particularly interesting, given their age.  Both are reflecting telescopes, meaning that they use mirrors rather than lenses to focus light.  Reflecting telescopes were rare in the eighteenth century because it was very difficult to manufacture a smooth mirror whose reflective surface was on top of, rather than underneath, the glass.  Having the reflective surface below a refracting layer of glass distorted the image; overcoming this was a technical challenge for those seeking to manufacture telescope mirrors.  These two telescopes are thus very early examples of reflecting telescopes, from an age when refracting telescopes using lenses were the norm.

Gregorian reflecting telescope, G. Adams, 1795.

Gregorian reflecting telescope, G. Adams, 1795. Van Vleck Observatory collections, Wesleyan University.

These telescopes are also interesting in that they are tabletop instruments.  Each is equipped with its own stand, as well as a set of knobs for adjusting the angle and position of the tube.  This suggests that these were designed as gentlemen’s telescopes, and perhaps that they came to the university as a part of a faculty member’s personal collection.  So far, we have not been able to locate any records of their purchase or use, although it seems possible that they were used as teaching tools.

Today, most of the large telescopes crowning remote mountaintops are reflectors, and many of them contain not just one primary mirror but several mirrors arranged in an array.  (Most of these very large mirrors are made at the Mirror Lab at the University of Arizona in Tucson—you can visit and take a tour to see the process yourself.) In that basic sense, these two little eighteenth-century telescopes are akin to the massive research instruments of today, even though they appear similar to the observatory’s 20-inch refractor.

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