The Lord sent thunder - קלת koloth, voices; but loud, repeated peals of thunder are meant.
And the fire ran along upon the ground - ותהלך אש ארצה vattihalac esh aretsah, and the fire walked upon the earth. It was not a sudden flash of lightning, but a devouring fire, walking through every part, destroying both animals and vegetables; and its progress was irresistible.

And Moses stretched forth his rod toward heaven,.... The same which Aaron had made use of before, but was now in the hand of Moses, and whose rod it properly was:
and the Lord sent thunder and hail, and the fire ran along upon the ground, hot thunderbolts, which struck their flocks, Psalm 78:48 and hail which fell so thick and weighty as to destroy both men and cattle, and break trees in pieces, and spoil the corn, the grass, and the tender herb; and fire, that is lightning, which descended so low, and in such quantities, as ran along the ground, and consumed all it met with. Artapanus (g), an Heathen writer, who speaks of this storm of hail, says, that Moses, besides the hail, caused earthquakes by night, so that those that escaped the earthquakes were taken away by the hail, and those that escaped the hail perished by the earthquakes, which he says overthrew all the houses, and most of the temples:
and the Lord rained hail upon the land of Egypt; upon Egypt, where rain was not common, and on all the land of Egypt, when in some parts of it it was scarce known, and hail as thick as rain; ice, snow, and hail, are most rarely if ever seen there, the air not being cold enough for the production of them (h). This was the Lord's immediate doing, when there was no likelihood of it, nor any appearance of second causes concurring to produce it, and came at the exact time he had foretold it should; all which were very extraordinary.
(g) Apud Euseb. Praepar. Evangel. l. 9. c. 27. p. 435, 436. (h) Vid. Scheuchzer. Physica Sacra, vol. 1. p. 139.