1893.] on Electrical Bailways. 53 



shock than man. It is not perhaps well known, but still a fact, that 

 a shock of 250 volts is quite sufficient to kill a horse almost instan- 

 taneously. 



The first model has a single overhead conductor with return by 

 the rails ; but in place of a single fishing-rod collector or trolley to 

 take the current from the overhead wire there are fixed on the car 

 two rigid bars, one at each end, which slide along the under surface 

 of the wire and make a rubbing contact against it. This system, 

 devised by Dr. John Hopkinson, has the advantage that there is less 

 difficulty in maintaining contact on uneven roads or on curves, and 

 that the catenaries of the suspended wire may be hung with greater 

 dip, and therefore with less tension. Again, the double contact 

 obviates the frequent breaks and consequent sparking of a single 

 trolley system. The second model shows the system adopted on the 

 City and South London line, and more recently followed on the 

 Liverpool Overhead line, of a conductor of channel steel, upon which 

 collectors fixed to the locomotives make a sliding contact. The 

 third track shows an overhead system like the first, but with an 

 insulated return in place of return by the rails. 



The characteristic feature of an electric motor is that it delivers 

 us the mechanical power we require directly in the form of a couple 

 about an axis instead of in the form of a rectilinear force, as is the 

 case with steam, gas, or air engines, w 7 hich must be reduced to a 

 rotary form by connecting rod and crank. Thus it is possible to 

 sweep away all intermediate gear, and to arrive at once at the 

 simplest of all forms of a traction motor, consisting of but one pair ■ 

 of wheels fixed on a single axle with the armature constructed directly 

 upon it, with its magnets suspended from it and maintained in their 

 position against the magnetic forces acting upon them by their 

 weight. Such a locomotive is shown in the third model before you. 

 So far as I am aware, a locomotive of such simplicity as this has 

 never been constructed for practical work, but on the City and South 

 London line the armatures of the motors are placed directly on the 

 axles, and the magnets suspended partly from the axles and partly 

 from the frame. 



The second model is an exact reproduction of the locomotives on 

 the City and South London line, but with a different arrangement of 

 motors. Here both armatures are included in the same magnetic 

 circuit, and both magnets and armatures carried on the frame of the 

 locomotive and not on the axles. The armatures are geared to the 

 axles by diagonal connecting rods, the axle boxes being inclined, so 

 that their rise and fall in the horn blocks is at right angles to the 

 connecting rods. This design, which is due to the late Mr. Lange, 

 of Messrs. Beyer, Peacock & Co., allows of the motor armature 

 being placed on the floor level of the locomotive, and so more easily 

 accessible. 



This model wall serve to show some of the characteristic features, 

 as well as some of the characteristic defects, of an electric motor as 



