Another of my little treasures. An 8 inch Ross (London) 'Concentric' lens. Brass barrel two element lens with a rotating disk to change aperture. Apertures marked 10, 19, 22, 27,32. Lens no. 51198 The Ross lens company was founded around 1830 and produced a range of quality lenses into the first half of the 20thC. I believe this one was made somewhere between 1890 and 1910, but it may be a bit earlier. It needs cleaning (dirt on the inside of the elements) but the glass looks relatively free of abrasion.