On the matter of the photoheliographs raised in the previous post, my colleague Graham Dolan informs me that one of the Dallmeyer photoheliographs was mounted on the 28-inch telescope on 12 October 1883 and removed on 24 April 1894, when it was placed on the south wing of the New Physical Observatory with a new equatorial mounting. This would suggest that when Christie ordered that the photoheliograph be placed on the south wing on 16 March, "at once" meant more than a month.
Part of the confusion about photoheliographs at Greenwich is because there were five identical instruments made for the 1874 transit of Venus expeditions. By 1894 three were floating about Greenwich, often with parts interchanged, and two were on loan - one to the Cape Observatory and one to the Science and Art Department. Most of one of these instruments is today mounted at the ROG in the Altazimuth Pavilion.