On August 31, 1830, he writes:-- I tried the Trio last Sunday and was satisfied with it, perhaps because I had not heard it for a long time.

I suppose you will say, "What a happy man!" Something occurred to me on hearing it--namely, that it would be better to employ a viola instead of the violin, for with the violin the E string dominates most, whilst in my Trio it is hardly ever used.

The viola would stand in a more proper relation to the violoncello.

Then the Trio will be ready for the press.
The composer did not make the intended alteration, and in this he was well advised.

For his remarks betray little insight; what preciousness they possess they owe for the most part to the scarcity of similar discussions of craftsmanship in his letters.