The velocity of light being 192,000 miles per second, and the mechanical value of sunlight incident perpendicularly on a square mile at the earth's distance being 83 × 5280 × 5280 foot pounds; the mechanical value of all the energy potential and actual, kept up in the space of a cubic mile by sunlight crossing it, is = 1200 ft. lbs. at the earth's distance. Similarly the mechanical value of a cubic mile of sunlight near the sun is found to be 1200 × 46,000=55,000,000 foot pounds.