The use of the word approbation in this sentence suggests that;
Approbation means approval, admiration, and praise. The readers of the text by Benjamin Franklin were impressed by the manner of his writing. According to more information obtained from the context, they even made guesses about who could have written such a wonderful text.
Those whom they guessed to be the writer of such a text were men of honor and this excited Franklin.
Summarily, Franklin's text impressed the readers and made them wonder who wrote it.
Learn more about the Autobiography of Benjamin Franklin here:
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