With regard to the speed of clipper ships, however, involving a rivalry far more thrilling and important than all the races ever sailed for the America's cup, the evidence is available in concrete form.
Lindsay's "History of Merchant Shipping" is the most elaborate English work of the kind.

Heavily ballasted with facts and rather dull reading for the most part, it kindles with enthusiasm when eulogizing the Thermopylae and the Sir Launcelot, composite clippers of wood and iron, afloat in 1870, which it declares to be "the fastest sailing ships that ever traversed the ocean." This fairly presents the issue which a true-blooded Yankee has no right to evade.

The greatest distance sailed by the Sir Launcelot in twenty-four hours between China and London was 354 knots, compared with the 424 miles of the Sovereign of the Seas and the 436 miles of the Lightning.

Her best sustained run was one of seven days for an average of a trifle more than 300 miles a day.

Against this is to be recorded the performance of the Sovereign of the Seas, 3562 miles in eleven days, at the rate of 324 miles every twenty-four hours, and her wonderful four-day run of 1478 miles, an average of 378 miles.
The Thermopylae achieved her reputation in a passage of sixty-three days from London to Melbourne--a record which was never beaten.