For large contact areas the magnetic system is found to be most economical, and this system might possibly be used to advantage to prevent slipping of short wire ropes and belts upon their driving pulleys, in cases where longer belts are inapplicable as in the driving of dynamos and other machinery. Experiments have also been, and are still being, made with the object of increasing friction by means of permanent magnetism, and also with a view to diminishing the friction of revolving and other moving surfaces, the results of which will probably form the subject matter of a subsequent paper.
Enough has been said to indicate that the development of these two methods of increasing mechanical friction opens up a new and extensive field of operation, and enables electricity to score another important point in the present age of progress. The great range and flexibility of this method peculiarly adapt it to the purposes we have considered and to numerous others that will doubtless suggest themselves to you. Its application to the increase of the tractive adhesion of railway motors is probably its most prominent and valuable feature at present, and is calculated to act as an important stimulus to the practical introduction of electric railways on our city streets, inasmuch as the claims heretofore made for cable traction in this respect are now no longer exclusively its own. On trunk line railways the use of sand and other objectionable traction-increasing appliances will be entirely dispensed with, and locomotives will be enabled to run at greater speed with less slipping of the wheels and less danger of derailment. Their tractive power can be nearly doubled without any increase in weight, enabling them to draw heavier trains and surmount steeper grades without imposing additional weight or strain upon bridges and other parts of the roadbed. Inertia of heavy trains can be more readily overcome, loss of time due to slippery tracks obviated, and the momentum of the train at full speed almost instantly checked by one and the same means.
Read before the American Association for the Advancement of Science. New York meeting, 1887.
ELECTRIC LAUNCH.
Trials have been made at Havre with an electric launch built to the order of the French government by the Forges et Chantiers de la Mediterranée. The vessel, which has rather full lines, measures 28 ft. between perpendiculars and 9 ft. beam, and is 5 tons register.
The electromotor is the invention of Captain Krebs, who is already well known on account of his experiments in connection with navigable balloons, and of M. De Zédé, naval architect. The propeller shaft is not directly coupled with the spindle of the motor, but is geared to it by spur wheels in the ratio of 1 to 3, in order to allow of the employment of a light high-speed motor. The latter makes 850 revolutions per minute, and develops 12 horse power when driving the screw at 280 revolutions. Current is supplied by a new type of accumulators made by Messrs. Commelin & Desmazures. One hundred and thirty two of these accumulators are fitted in the bottom of the boat, the total weight being about 2 tons.
In ordering this boat the French government stipulated a speed of 6 knots to be maintained during three hours with an expenditure of 10 horse power. The result of the trials gave a speed of 6½ knots during five hours with 12 horse power, and sufficient charge was left in the accumulators to allow the boat to travel on the following day for four hours. This performance is exceedingly good, since it shows that one horse power hour has been obtained with less than 60 lb. of total weight of battery.