The ledger show what appears to be the completion date of each lens. So we know 1559 (the serial number at which the ledger starts) was completed on 7th December 1863 and the last recorded lens is 3733 which was finished on 14th January 1877. So yes, certainly sequental. There are later 'anomalies' in that some Petzvals (oddly enough sold as projection lenses for a Triunial Lanter) were sold much later under Sir Howard Grubb's name in the 1890s and it is possible that they were old lenses which were finalised much later as they have much later serial numbers and the lantern has a mix of previously finished, early and later lenses! But the ledger is clear enough.
FWIW Willeica and myself conjectured at length over the serial numbers and the first series of lenses appear to end in the early 4000s, then a second, much smaller set of lenses have serial numbers in the very low 5000s. It looks as though in between records may have been lost and a new sequence initiated, but this remains conjecture and if serial numbers in the high 4000s turn up it will be wrong. Given the very low numbers of lenses bactch built (sometimes even single lenses were made, I'd suggest that yours was built to order. The fact that the adverts list a C1 as a rigid lens (like yours) suggests that options were available. FWIW the brasswork of Grubb lenses seems to have been slightly variable and threads aren't always interchangeable although they were evidently meant to be. So handmade and a customer's requirements could have easily been catered for as a result.
I suspect that very few of the larger lenses were ever made. One of the reasons may well be that obtaining good quality glass in larger sizes was difficult - this was especially true for the even larger telescope objectives.
Bookmarks