p. 290
तच्छुक्रं ज्योतिषां मध्येऽतप्तं तपति तापनम् ॥
In plain words
That pure blaze, standing in the middle of all the lights, is itself never heated by anything — and it burns, the burner of them all.
Close to the Sanskrit
That radiance, in the midst of the lights, unheated, burns — the heater.