In his book, A Tour in Germany, and some of the Southern Provinces of the Austrian Empire, in 1820, 1821, 1822, published in Edinburgh in 1824, Sir John Russell describes Beethoven in 1821:

The neglect of his person which he exhibits gives him a somewhat wild appearance.  His features are strong and prominent; his eye is full of rude energy; his hair, which neither comb nor scissors seem to have visited for years, overshadows his broad brow in quantity and confusion to which only the snakes around a Gorgon’s head offer a parallel.  His general behaviour does not ill accord with the unpromising exterior.  Except when he is among his chosen friends, kindliness or affability are not his characteristics.  Even among his oldest friends he must be humoured like a wayward child.  He has always a small paper book with him, and what conversation takes place is carried on in writing.  In this, too, although it is not lined, he instantly jots down any musical idea which strikes him.  These notes would be utterly unintelligible even to another musician, for they have thus no comparative value; he alone has in his mind the thread by which he brings out of this labyrinth of dots and circles the richest and most astounding harmonies.  The moment he is seated at the piano, he is evidently unconscious that there is anything in existence but himself and his instrument; and, considering how very deaf he is, it seems impossible that he should hear all he plays.  Accordingly, when playing very piano, he often does not bring out a single note.  He hears it himself in the “mind’s ear.”  While his eye, and the most imperceptible motion of his fingers, show that he is following out the strain in his own soul through all its dying gradations, the instrument is actually as dumb as the musician is deaf.  It is exceedingly difficult to prevail upon him to perform, as he has a perfect horror of being exhibited; but when he does place himself at the piano, it is interesting to observe how the music of the man’s soul passes over his countenance.  He seems to feel the bold, the commanding, and the impetuous, more than what is soothing or gentle.  The muscles of the face swell, and its veins start out; the wild eye rolls double wild; the mouth quivers; and Beethoven looks like a wizard, overpowered by the demons whom he himself has called up.

Cited in: Marek, George (1969) Beethoven: Biography of Genius. London: William Kimber, p.566.