What does "Rubber off of dust" mean?
Mr. Duane told me at the Funeral of our late virtuous and able President1 that he, Mr. Duane, had accustomed him self to read the Year Books. Mr. De Lancey who was C[hief] J[ustice] of N. York he said advised him to it, as the best Method of imbibing the Spirit of the Law. De Lancey told him that he had translated a Pile of Cases from the Year Books, altho he was a very lazy Man.
Duane says that Jefferson is the greatest Rubber off of Dust that he has met with, that he has learned French, Italian, Spanish and wants to learn German.
Duane says, he has no Curiosity at all—not the least Inclination to see a City or a Building &c.Diary of John Adams, Volume 2, 1775
Does the dust refer to the layer of dust that accumulates on books that nobody reads, i.e dusty volumes? One could be a sweeper or someone who dusts or brushes off something.
But why Rubber off of dust? Does one rub off dust? It is something I cannot get my head around.
Solution 1:
I think your first impression is correct -- "Rubber off" would be more clearly rendered as Rubber-off.
In this paragraph:
Duane says that Jefferson is the greatest Rubber off of Dust that he has met with, that he has learned French, Italian, Spanish and wants to learn German.
Duane (who I guess is James Duane of the First Continental Congress) is characterizing Thomas Jefferson as someone who pulls all sorts of dusty old books down from the shelf to read them.
When you pull a dusty old book down off a shelf, you are likely to give it at least a cursory cleaning, at least to get the worst of the dust off.
Jefferson is famous as a polymath -- someone who delved into, and mastered, all sorts of subjects. And so it shouldn't surprise anyone that he was a voracious reader. One famous story has Jefferson basing the structure of the Declaration of Independence off of Euclid's Elements.
Now for the following passages:
Duane says, he has no Curiosity at all—not the least Inclination to see a City or a Building &c.
That his Memory fails, is very averse to be burthened. That in his Youth he could remember any Thing. Nothing but what he could learn, but it is very different now.
I've added the sentence after your quote because it underscores that Duane is now talking about himself, in contrast to Jefferson. In his old age(42), Duane has lost the youthful curiosity that Jefferson (32) still possesses.
Whether Duane is simply amazed at Jefferson's energy, or whether he's being scornful of "book larnin'" his statements underscore the idea that dust is being rubbed off of books.
Solution 2:
Rubber off of dust may be taken more than one way. It could mean one who makes an idea or thought seem more attractive as described here.
It is briefly the function of such study to rub off the dust which makes the gold less attractive than the base metal gilt.(The Study of English Literature: Three Essays)
This may be extended to a person who finds a value under the dust, as here.
Then shall we often rub off the dust and rust from what seemed to us but a common token, which as such we had taken and given a thousand times; but which now we shall perceive to be a precious coin,(The Study of Words By Richard Chenevix Trench)
The idea of renewal is here
In short, there is abundant proof, that in our conversation we were yielding to the spirit of the mountain; to the genius of the place; and rubbing off the dust of our studies among the wilds of Eryri.(The Passengers: Containing, The Celtic Annals By John Parker)
and here.
...a Receipt from from Bachop for a paper bundle and four Hogsheads of Porter, which will rub off the dust and brighten my end of the Chain. And I shall hereafter keep it always Clean and bright.(The Papers of Henry Laurens, Oct. 1769)
Given the context in Diary of John Adams, the rubber off of dust probably is the one who finds value under the dust, or, is not allowing dust to cover that which is useful. The contexts suggests Jefferson was not the one to let dust cling to the means of learning (books, etc), but rather the one who learns.
The learning means use of the books, and use means the dust is constantly rubbed from them.