Chiefly owing to the brittleness of this material, Lord Rosse's first larger specula were composed of a number of thin plates of speculum metal (sixteen for a 3-foot mirror) soldered on the back of a strong but light framework made of a peculiar kind of brass (2.75 of copper to 1 of zinc), which has the same expansion as his speculum metal.
1-4), and later Lord Rosse's 36-in.
In Lord Rosse's instrument (also of the Newtonian type) the observer is suspended in a cage near the eye-piece, and the instrument is used in the open air.
Educated at Trinity College, Dublin, he was appointed in 1865 assistant to the Earl of Rosse's observatory at Parsonstown, and whilst there he discovered four spiral nebulae.
Rosse's determinations, like those of his predecessors, were made with the thermopile.