18th Century Telescope by Jesse Ramsden
This is a great example of a late 18th century telescope by the famous
instrument maker Jesse Ramsden. He was born in Halifax in 1731 and he died in Brighton in 1800. All of his work is of
the highest standard, which is evident when using this telescope. The achromatic objective lens is shown above in its brass
surround. This unscrews using the knurled ring to allow access to the back of the glass for cleaning.
Ramsden employed over 50 men, but he was said to have undertaken the construction of the most delicate instruments himself.
The telescope is made of brass and mahogany. These were typical telescope making materials from the 18th century, especially for marine use. The photograph above shows the barrel, and the screws that attach the wood to the brass. At the front there are four screws, and at the opposite end of the barrel there are six screws.
Not only is this telescope in superb working order, it also has its original leather case. I believe that it is original as it fits so well and slides in and out very smoothly.
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The eyepiece end of the telescope is shown in the two photographs above. The protective shutter rotates around a pivot and does not slide along straight tracks. The eyepiece design employed is known as the "Ramsden" as it was developed by Ramsden earlier in his life. A variation of Ramsden style eyepieces, the Kellner, is still used in telescopes today.
The engraved signiture on a telescope is usually the main way of dating it. This signiture runs from the eyepiece towards the barrel which helps us to date it to the 1790's. It reads:
Je Ramsden London
Above is the telescope fully extended showing its three draws. The
telescope measures 9 3/8" at its smallest, and 29" when fully drawn out. The case measures 10" in length.
All of Ramsdens instruments were of the highest standard, and he was highly commended for this in 1787 by J.D. Cassini,
who bought instruments for the Paris Observatory. He wrote of Ramsden:"I have been able to give you a very inadequate picture
of the admiration which the sight of the splendid instruments made in England by the famous Ramsden roused in us. The richness
of this artist's creative genius, the perfection of his execution, and his wide experience, force me to recognise that it will be
a long time before anyone is able, I do say to surpass, but even to equal his achievement."
Ramsden's work was widely recognised, and he even supplied a hand held telescope to Admiral Lord Nelson!
Piazzi discovered asteroid (1) Ceres using the Ramsden vertical circle of the Palermo Observatory in Italy.
The first Ordnance Survey of Britain was produced using Ramsden's theodolite.
Another famous name who Ramsden made Instruments for is Captain Cook. Below is his sextant, made by Ramsden around 1770.
Of his three expeditions, four sextants remain. Click on the picture for a larger view.
Photograph: National Maritime Museum
