Many persons suppose, and maintain, that the grandeur of the monuments of the ancients, and the great size of the stones they employed for building purposes, prove that they understood mechanics better than the moderns. The least knowledge in mechanics, however, will show this opinion to be erroneous. The moderns possess powers which were unknown to the ancients, as the screw, and the hydraulic press, the power of which last is only limited by the strength of the machinery. The works of the ancients show that they expended a vast deal of power and labor to gratify the pride and ambition of kings; but the moderns can do all these things much easier, and in far less time, whenever they deem it proper. There was nothing in ancient times to be compared with that daring, ingenious, and stupendous monument of engineering skill—the Britannia Tubular Bridge, across the Menai straits—projected, designed, and built by Robert Stephenson, the famous English engineer. He had previously built a similar but smaller structure—the Conway Tubular Bridge.