Then the storm bursts. We can hear it rolling in the short periods, mostly uniform in structure and grouped in verses of two clauses each, the second of which echoes the first, like the long-drawn roll that pauses, slackens, and yet persists. Seven times "the voice of Jehovah" is heard, like the apocalyptic "seven thunders before the throne." The poet's eye travels with the swift tempest, and his picture is full of motion, sweeping from the waters above the firmament to earth and from the northern boundary of the land to the far south. First we hear the mutterings in the sky (ver. 3). If we understood "the waters" as meaning the Mediterranean, we should have the picture of the storm working up from the sea; but it is better to take the expression as referring to the super-terrestrial reservoirs or the rain flood stored in the thunder-clouds. Up there the peals roll before their fury shakes the earth. It was not enough in the poet's mind to call the thunder the voice of Jehovah, but it must be brought into still closer connection with Him by the plain statement that it is He who "thunders" and who rides on the storm-clouds as they hurry across the sky. To catch tones of a Divine voice, full of power and majesty, in a noise so entirely explicable as a thunderclap, is, no doubt, unscientific; but the Hebrew contemplation of nature is occupied with another set of ideas than scientific, and is entirely unaffected by these. The psalmist had no notion of the physical cause of thunder, but there is no reason why a man who can make as much electricity as he wants by the grinding of a dynamo and then use it to carry his trivial messages should not repeat the psalmist's devout assertion. We can assimilate all that physicists can tell us, and then, passing into another region, can hear Jehovah speaking in thunder. The psalm begins where science leaves off.