From Janet Gunn, Nokesville, Virginia, US
You mentioned that building a liquid mercury telescope was first attempted in the late 19th century, but didn’t give any more details.
I remember reading some time ago about a liquid mercury mirror telescope built in the 19th century by William Parsons, 3rd Earl of Rosse, at Birr Castle in Parsonstown, Ireland. It was reported that a horse trotting down the road a mile away could cause vibrations that negatively affected the mirror. Parsons was also responsible for building, in 1845, the 72-inch conventional reflector telescope known as the Leviathan of Parsonstown, which helped to identify the first spiral nebulae.
