the one hand, and the to-be-thought, on the other, traces back to the difference between being and beings; because, moreover, this difference is operative everywhere in Occidental history but is the least questioned and least thought-through, and is never taken as the difference that it is; for all of these reasons, the insertion of numbered fragments into Heraclitus’s thinking—that is, into that which he thinks —must necessarily remain obscure. First we must learn what the to-be-thought is in Heraclitus’s thinking. Therefore, the second part of the saying in that fragment that is numbered 51 is initially taken by us as the most important part. Here something essential is said regarding ἁρμονία, i.e., regarding the essence of φύσις:
παλίντονος ἁρμονίη ὅκωσπερ τόξου καὶ λύρης.
The jointure (namely, the self-differentiating) unfolds drawing-back, as shows itself in the image of the bow and lyre.
We spoke about the ‘bow’ and the ‘lyre’ at the beginning of this lecture course when we made reference to the goddess Artemis, whom we claimed to be the goddess of Heraclitus. Her essence shows itself in the bow and lyre. Now we learn that the essence of the to-be-thought, and thus of what Heraclitus thinks—namely, φύσις as ἁρμονία—reveals itself in the bow and lyre. Can we doubt any longer that Artemis is the goddess of Heraclitus? Will we recognize that Heraclitus, not as an Ephesian but as a thinker—and, indeed, as an inceptual thinker—is beckoned in his thinking by this goddess? The emerging that unfolds (in that it originates from self-concealing) brings itself into separation, in a way, from self-concealing. Emerging thereby appears to move away from submerging, and is thus determined by a closing-together and a self-closing, just as the one end of the relaxed bow springs away from the other so that the curvature of the bow (and thus the bow itself) disappears. Emerging, taken on its own terms, seems like the mere bending away from one another of the ends of a relaxed bow. In truth, however, emerging is what shows itself to us in the image of the tightened (and that means, at the same time, tensible) bow. It belongs to the essence of the bow that while the ends stretch away from one another they, at the same time and within this very stretching away, are stretched back toward one another. Emerging does not abandon submerging and unhitch it: rather, in emerging, emerging itself  submerges into self-concealment as the facilitator of its essence and yokes itself to it. φύσις is this moving ‘away’ and moving apart of self-opening and self-closing, as well as the ‘return’ of each into being toward-one-another. φύσις is the to-and-fro, the back-and-forth: ἁρμός /the counter-moving joining/ἁρμονία /‘jointure.’ But inasmuch as λύρα (the lyre) is named, the thinker, by means of a single image in which the bowed-ness and counter-striving are one with the jointure, grasps ἁρμονία, in which the special form of harmony appears. The goddess whose signs are bow and
Heraclitus: The Inception of Occidental Thinking
GA 55 p. 152