It is acknowledged that the steam yacht Voyageur de la Mer, built at Boston for the Pasha of Egypt, lias proved a failure. About the why and the wherefore of this, there are two sides to the story. One side is that the failure was caused by defective boilers, which were made in New York ; the other side is, that it was owing to defective machinery, which was built in Boston. A correspondent from Medf ord, Mass., who is a ship-carpenter, informs us that the model of this vessel is good, having been drafted by Samuel Pook, Naval Architect, Boston, but that both boilers and machinery are defective. We sincerely regret that any vessel built in our country for a foreign potentate or plebeian should (as in this case) have tarnished the reputation of our American engineers.