I recently bought an early Petzval lens engraved Horne & Thornthwaite, 123 Newgate Street with the serial number 1345.
Horne & Thornthwaite operated from Newgate Street from 1854 onwards, before that date they were operating from that address as Horne, Thornthwaite & Wood.
I disassembled the lens to clean the elements and discovered a pencilled inscription around one of the rear pair of elements saying "Horne, Thornthwaite and Wood"
It seems to me likely that this lens was produced at just about the period that Wood left the partnership. The optics were assembled while Wood was still there, but the lens barrel seems to have been engraved after his departure, presumably later in 1854 or early in 1855.
This is useful information as the lens Vade Mecum can only hazard a guess that several lenses with serial numbers in the 3000s date to 1858.
Seán
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