Here again one meets the familiar safeguard against accident. Some engineer of one of these towing locomotives might sometime overload it, so the power of doing so has been taken out of his hands. On the windlass or drum that holds the towing hawser there is a friction coupling. If the engineer should attempt to overload his engine, or if for any other reason there should suddenly come upon the locomotive a greater strain than it could bear, or upon the track, or upon the hawser, the friction clutch would let loose at its appointed tension of 25,000 pounds, and all danger would be averted. When the locomotives are towing a ship from the walls it is natural that there should be a side pull on the hawser. This is overcome by wheels that run against the side of the track and are mounted horizontally. All of the towing tracks extend out on the approach walls of the locks so that the locomotives can get out far enough to take charge of a ship before it gets close enough to do the locks any damage. [Illustration: A _Mauretania_ IN THE LOCKS] From the foregoing it will be seen that a great deal of electric current will be required in the operation of the locks. This will be generated at a big station at Gatun, with a smaller one at Miraflores, and they will be connected. The overflow water will be used for generating the required current, and in addition to the operation of the lock machinery it will operate the spillway gates, furnish the necessary lighting current, and eventually it may furnish the power for an electrified Panama Railroad. In passing a ship through the canal it will be necessary to open and close 23 lock gates, of an aggregate weight of more than 25,000 tons, to lower and raise 12 fender chains, each weighing 24,000 pounds, and to shut and open dozens of great valves, each of which weighs tons. All these operations at each set of locks will be controlled by one man, at a central switchboard. In addition to these operations there is the towing apparatus. The arrangement at Gatun is typical; there 4 fender chains must be operated, 6 pairs of miter gates, and 46 valves. In all not less than 98 motors will be set in motion twice, and sometimes this number may be increased to 143. Some of them are more than half a mile away from the operator, and half of them are nearly a quarter of a mile away. The operator in his control house will be high enough to have an uninterrupted view of the whole flight of locks over which he has command. His control board will consist of a representation of the locks his switches control. On his model he will see the rise and fall of the fender chains as he operates them, the movement of the big lock gates as they swing open or shut, the opening and closing of the valves which regulate the water in the culverts, and the rise and fall of the water in the locks.