Art History Gallery on Instagram: "John Martin (1789-1854): Seventh Plague of Egypt, 1823, Oil on canvas, 144.1 x 214 cm, Museum of Fine Arts, Boston . . In the Bible, Moses calls down ten plagues before the pharaoh is persuaded to free the enslaved Israelites. This work, one of Martin's grandest paintings, depicts the seventh: "And Moses stretched forward his rod toward heaven, and the Lord sent thunder and hail, and fire rained down onto the earth." Moses and his brother Aaron are at the…