Gross darkness

A Rhondda coal-miner who had become a lay preacher one Sunday took as his text

"For behold the darkness shall cover the earth and gross darkness the people" (Isaiah 60, 2).

"When any of you miners are in the last seam and the lamp goes out, that's darkness", he said.

"But what should we understand by gross darkness?

Now when I was at school; I was taught that a gross is 144 and accordingly you will understand that gross darkness is 144 times darker than darkness."