The Mystery Object Revealed

As I revealed this afternoon in my talk at the Royal Astronomical Society, yesterday’s mystery object..

..is in fact the 4-inch object (geddit?) glass that was manufactured by Howard Grubb in Dublin and taken to Sobral in Brazil in 1919 to be used in a famous experiment to measure the bending of light by the Sun during a total eclipse.

Here is a picture of the observing setup in Sobral:

The 4-inch lens is mounted in the square tube on the right. The eclipse was observed using a coelostat (a steerable mirror) that reflected light into the telescopes. Here is a photograph of the coelostat:

The object glass and coelostat are usually on display at Dunsink Observatory but these are currently en route to Brazil for the commemorations of the centenary of the historic expedition.

Photo Credits to Tom Ray of DIAS…

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