very old equipment term

[Brian W (Brian)]

Hi all, on Feb 11, 1806 Sir W. Herschel was observing M-42 with a '10 foot reflector and a double eyepiece'.

I am guessing that 10 foot refers to the diameter but the term 'double eyepiece' leaves me totally baffled!

Any ideas?
Brian

[gbeal]

Likely a two lens eyepiece, Al Nagler hadn't invented his trademark sample then, LOL.

[acropolite (Phil)]

I expect 10 foot would be the focal length.

But William knew he could build a bigger mirror, and followed that with a telescope with a mirror diameter of 9 inches (22.5 centimeters). As the mirror size increased, so did the length of the telescope, to 10 feet long.

here are some descriptions

[DavidU (Dave)]

Probably not the Huygens as it was the 1800's but prob the Ramsden eyepiece.

[Brian W (Brian)]

well so much for my guess what the ten foot referred to. I will look up the Ramsden ep.

Thanks,
Brian