Third 2 33 = 23·53} Fourth 2 55 = 20·57} Mean of second pair = 22·05 Fifth 2 30 = 24·00} Sixth 2 56 = 20·45} Mean of third pair = 22·23 giving as a mean 21·93 knots per hour, or 25-1/4 statute miles. The boat was fully equipped for active service, i.e. with a load of 6-3/4 tons on board. It was found during the trial that at speeds of 17 and 19 knots the vibration of the boat was considerable, but when running over 20 knots it was hardly perceptible; the excessive vibration taking place when the revolutions of the engines became a multiple of the natural vibration of the boat. Torpedo boats are at the present time being built by this firm for the English, French, Spanish, Austrian, and Italian governments. _Russian Torpedo Boats, built by Mr. S. Schibau, Prussia._--Mr. S. Schibau, of Elbing, Eastern Prussia, in 1878 constructed ten torpedo boats for the Russian government, similar to the one shown at Fig 163. These boats are each 66 feet long, and 11 feet 3 inches beam. They are built of steel plates about an eighth of an inch thick. Their engines consist of three cylinder compounds, with surface condensers; and they run at 380 revolutions per minute, at full speed, driving a screw 4 feet in diameter. They have been variously armed, some with the spar, some with the Whitehead fish, and some with the Harvey towing torpedo. Their speed is about 18 knots per hour. _Messrs. Herreshoff's Torpedo._--Messrs. Herreshoff, of Rhode Island, U.S.A., have also constructed several torpedo boats. One of these, built for the English government, is shown in section at Fig. 164. This boat is 59 feet 6 inches long, 7 feet 6 inches beam, and 5 feet 6 inches deep; she draws about 1 foot 3 inches of water. [Illustration: RUSSIAN TORPEDO BOAT, HERRESHOFF'S TORPEDO BOAT. PLATE LI]