Lean, bent slightly backwards, and with an elongated neck, Furtwängler in front of an orchestra gave the impression of overlooking vast spaces. His beat had very little in common with that of present-day conductors. In stretches of pianissimo it could be minute and extremely precise; elsewhere, outstretched arms undulated downwards in total physical relaxation, so that the orchestra had to guess where the beat should be. The sounds thus produced could be of an elemental intensity that I have not experienced since. The image of ‘Jupiter tonans’ was what came to me then: Furtwängler’s thunder was always preceded by lightning-shaped movements, which made the orchestra play considerably after the beat (if there was a beat), and induced double-basses and cellos to prepare the ground for the sonorities by discreetly anticipating their entry. Arthur Nikisch, according to Furtwängler, was the only conductor who presented a thoroughly unforced appearance; Furtwängler regarded himself, in this respect, as Nikisch’s pupil, and believed that any contraction of muscle on the part of the conductor would show up in the sound of the orchestra as if reproduced on a photographic plate.
Furtwängler’s technique, though seemingly unfocused and impractical, was in fact well considered. Not only did it help to anticipate the quality of sonorities and the delay of an important beat: it also foreshadowed changes of atmosphere or the gradual modification of tempo. And this leads us to Furtwängler’s particular strength: he was the great connector, the grand master of transition. What makes Furtwängler’s transitions so memorable? They are moulded with the greatest care, yet one cannot isolate them. They are not patchwork, inserted to link two ideas of a different nature. They grow out of something and lead into something. They are areas of transformation. If we observe them minutely, we notice that, at first almost imperceptibly, they start to affect the tempo, usually a great deal earlier than is the case with other conductors, until their impact finally makes itself felt. Even where I disagree with the amplitude of Furtwängler’s tempo modifications — as in the first movement of Beethoven’s Fourth Symphony — I do not know what to admire more: the urgency of his feeling or the acuteness of his control.
Alfred Brendel, “Furtwängler”
What I wonder, after reading this, is whether the controlled/uncontrolled dichotomy is the wrong one to apply to modern conductors vs. Weingartner, Mengelberg, Stokowski, early Celibidache, etc. I would say that Furtwängler was completely in control of what effect free bowing would have, for example, and could marshal that in a less nitpicky way to shape the larger structure of a piece. Such practices have just fallen out of style, unfortunately; the vocabulary has become more limited.