Adam Clarke on Genesis 42:1

Jacob saw that there was corn - That is, Jacob heard from the report of others that there was plenty in Egypt. The operations of one sense, in Hebrew, are often put for those of another. Before agriculture was properly known and practiced, famines were frequent; Canaan seems to have been peculiarly vexed by them. There was one in this land in the time of Abraham, Gen 12:10; another in the days of Isaac, Gen 26:1; and now a third in the time of Jacob. To this St. Stephen alludes, Act 7:11 : there was great affliction, and our fathers found no sustenance.