After discussing with Robert Adelson regarding a harp I'm currently restoring, he suggested to write in this forum to hear different opinions.
The harp is an Erard Empire simple-action, with soupape. The plate doesn't bear any number whatsoever
I think this instrument is almost identical to the harp number 7 held in the Musée de la musique in Paris because of the same mechanism, decoration and style
Apparently these two instruments should be of the same period but the soupape of mine left me quite puzzled as its hinges are on the other side of every other harp I have ever seen before
I was wondering if this instrument was a kind of an experiment so built before the first harp made in 1799, as it has the fourchettes outside of the plate as in the patent of 1794. The harps made before this kind of mechanism, which were made between 1786 and 1794 had the fourchettes inside, like the so called "prototype" number 1 which was in the Érard collection and now at the Musée in France. Thanks to the letters contained in the book "The history of the Erard piano and harp in letters and documents" by Adelson et al, we know that Sébastien was already building several harps in 1791 with the new mechanism, he was surely referring to the fourchettes but we cannot know if they were inside the plate or outside. By the pictures found its plausible to say that the first harps ever made were like the prototype, and that from a certain later moment the harps were like mine and number 7, which is referred to as Grand Modèle
About my harp the only number I could find was the roman number III inside the harp in places almost impossible to see without disassembling it, as the inner side of the two plates, the base and the mechanism itself
Usually even in cases of multiple numbers inside of a harp, as with modern ones with a number for the mechanism and another for the woodwork (which is the same of the register), the numbers are always hindu-arabic. As Lewis Jones pointed out in abother article, the internal numbers, which could be even three different ones, were probably used for internal use during production. Robert also told me that Panagiotis Poulopoulos made an article regarding multiple numbers in ancient harps. I actually believe that this harp might be the third ever made with the fourchettes outside, before starting the ledgers, as a prototype because on the taquet and in its slot there is the same number III
The number on the taquet of all the harps has always been the same of the harp itself on the plate. I also discovered that in the later empire, 1810s and further, there used to be small circles on it beside the number. I believe that in that case the circles could have been used for assemblying the harp with the right pieces during production.
Another possible explanation could be that this instrument is number 3 of the ledger, in which there is a blank space, but used as an instrument to be rented and never sold.
I'm asking to you all if anyone has any other clue about the number and date of this instrument, about the signs on the taquet and also if anyone has any picture of harps bearing numbers around 7 if they could provide them.