Exodus 10:21

And the Lord said unto Moses ,.... About the eleventh day of the month Abib:

stretch out thine hand toward heaven ; where the luminaries are, and from whence light comes:

that there may be darkness over the land of Egypt, even darkness which may be felt ; that is, what caused it, the gross vapours and thick fogs; for otherwise darkness itself, being a privation of light, cannot be felt: Onkelos paraphrases it,"after that the darkness of the night is removed;'so Jonathan; that it might appear to be different from that, and be much grosser.