742 EEPOET— 1889. 



required for workinty her. The first of these is to put the current on or off; the 

 second for half or full speed ; the third for going ahead or astern. The first is 

 mecbanically locked with the others, so that they cannot be moved without first 

 cutting ofi' the current. Fusible cut-outs are inserted in the circuit, so that if the 

 propeller become jammed by weeds the motor will not be burnt up. The speed of 

 revolution of the motor, which is coupled direct to the propeller, is 720 revolutions 

 per minute for full speed and 510 for half speed. The full speed is only between 

 five and six miles an hour. This is really fast enough for ordinary work ; 

 it is only where there is a strong stream that it is sometimes a little tedious 

 creeping up for half an hour. The speed might be increased by putting in more 

 accumulators, which the launch could easily carry under the floor without over- 

 loading. At present the batteries are all under the seats on each side of the boat. 

 Thus the whole space is clear for passengers, of which she could easily carry twenty. 

 It is clear that the electric launch has a great advantage over the steam launch. If 

 we reckon the size of launch by the number of passengers it will hold, the electric 

 launch is the cheaper. 



The author spent one day in testing the performance of the launch on a trip 

 of nearly 3U miles. Starting from the house at Bray at 11.45 a.m. the time was 

 taken, and allowance made for all the locks passed through and other stoppages. 

 At 4.1 P.M., near Hambledon Lock, the return journey was commenced, and, stop- 

 ping an hour at Medmenham Abbey, home was reached at 7.48 r.M. During the 

 outward journey allowance for locks was made by distance. On the return this 

 allowance was estimated by time. Thus on the outward journey the average speed 

 was 1 mile in 11'3 nunutes, and on the homeward journey in 10'2 minutes. The 

 average of these is 790 feet per minute. On arrival at home the stern was attached 

 to a spring balance connected by a rope with the shore. The pull at full speed was 

 97 lbs., which, though not accurately, still approximately gives the pull when 

 the motor is going at the same speed while the launch is going on. This gives 

 1*44 horse-power or 1,074 watts, including electrical losses, slip, and all friction. 

 The average pressure at the motor terminals during the run was 78 volts, and the 

 average current 23 amperes, which gives 1,794 watts expended. This gives a total 

 efficiency of 60 per cent. This is not at all bad, and promises well for the future. 



The author suggested that, in order to supply the enormous demand which will 

 exist after a few years for charging stations, negotiations should be opened with 

 the Thames Conservancy, and also with millowners at the weirs, to establish 

 charging stations with water-power at nearly all the weirs, and thus to establish 

 the most perfect system of pleasure-launching in any part of the world. 



5. Series Electrical Traction (Nortlifleet Tramways). 

 By Edward Manville, M.I.E.E. 



The expenses of horsing a tramway form such a serious proportion of the total 

 working expenses that any cheaper effective method of propulsion will naturally be 

 gladly received by the various companies. 



Many leading authorities in tramway admiuistration who have tested and 

 considered the various methods of tramcar propulsion have of late publicly ex- 

 pressed their confidence in the great suitability and economy of electricity for the 

 purpose. 



It is obvious that, iu any systems of mechanical traction requiring the distribu- 

 tion of power over many miles of line, the maximum economy is attained when 

 all the power is developed at one station. 



The economical distribution of electrical power over long distances necessarily 

 involves the use of current at high potential, though at the same time it is dangerous 

 to permit large differences of potential at the terminals of motors running in 

 parallel, both in respect of manipulation and the preservation of the motors from 

 injury ; but if the motors are run in series these difficulties disappear, and the 

 advantages of high potential are secured. 



The extension of the Gravesend, Rosherville, and Northfleet tramways, 

 equipped upon the Series system, was opened in March last. 



