The sun-dial of Ahaz. We are informed by Herodotus that the sun-dial was an invention of the Babylonians (Herod; 2.109), from whom it would readily pass to the Assyrians. Ahaz may have obtained a knowledge of it, or an actual specimen, when he visited Tiglath-Pileser at Damascus (2 Kings 16:10), and, on his return to his capital, have caused one to be erected there.
Sun-dials are of several kinds. The one here spoken of seems to have consisted of a set of steps, with a perpendicular gnomon or pole at the top, the shadow of which receded up the steps as the sun rose in the heavens, and descended down them as the sun declined.
We must suppose that the sign was given in the forenoon, when the shadow was gradually creeping up the steps. Hezekiah thought that a sudden jump in the same direction would be as nothing compared with a reversal of the motion, and therefore required that the shadow should go back, which it did.
How the effect was produced, whether by an eclipse as argued by Mr. Bosanquet, or by refraction, or by an actual alteration of the earth's motion, we are not told; but there is reason to believe that the cause, whatever it was, was local, not general, since the King of Babylon subsequently sent ambassadors, to inquire concerning "the wonder that was done in the land" (2 Chronicles 32:31).
The sun returned ten degrees. We must not press this expression as indicating a real alteration of the sun's place in the heavens. The meaning is that the shadow cast by the sun returned.