Alright - I know i'm supposed to be the "expert" on weird old lenses, but this one is just - too weird even for me:
It's a "Thomson Brothers, London" set with a barrel and five lens cells. The cells are only marked 1, 2, 3, 4, and 5. Cells no. 1 and 3 have a shiny brass ring that might indicate that they're supposed to be front cells.
Focal lengths are (assuming Fl in inches):
Using cell 2 as a rear cell gives a very clear image with very good field flatness. Cell 4 gives a more curved image plane, also clearly visible without front cell. Cell 5 gives the most curved image plane I've ever seen, and no "mismounting" of any other lens cell I have is anywhere near as bad. To add to the conundrum cells 1-4 are two cemented elements, while no. 5 is a triplet...
I can only assume that this extreme field curvature was made on purpose, and the difference in the construction was done to make it even worse! So could this be made as a set for landscape and portrait work, where cell 5 was intended for portraits, 2 for landscapes, and 4 for more "general use" (and wider angle)?