This is drawing of the photographic pier shows the plateholder with the glass reticle directly in front, seen here in the direction from which the plates were exposed. On top is a spirit level and at the bottom the plumb bob hanging from a thin silver wire, steadied by immersion in a glass jar filled with water. An image of the reticle and silver wire was recorded, superimposed on that of the Sun, as can be seen in this image (9k.jpg). Another image of plate taken at the Vassar College of the 1882 transit is here (9k.jpg).
Newcomb Simon - Observations of the Transit of Venus, December 8-9, 1874 - 1880
Sky and Telescope, February 1961, 86
to 1882 TOV page