Light speeds

"Light consistently travels at 186,000 miles per second."

Quoth Robert L. Wolke (What Einstein Told His Barber), "When people talk about the 'speed of light as being 186,000 mps they should always be careful to add 'in a vacuum.'" Because when light enters a transparent medium it slows down...The speed of light in water, for example, is only three-quarters as fast as it is in the air."