PRESIDENTIAL ADDRESS. 593 
weight of the locomotive in comparison with its tractive force and power, As 
an example, we may take the Giovi line in Italy, where steam trains, consisting 
of 310 tons of rolling-stock and 202 tons of locomotive (one in front and the other 
at the back), have been replaced by three-phase trains, consisting of 380 tons of 
rolling-stock and two electromotives, each weighing 60 tons (also placed front 
and rear). Thus there has been a saving in total weight of 12 tons, and at the 
same time an increase in useful weight hauled of 70 tons. The average grade 
of this line, over which passes the whole traftic between the Port of Genoa and 
the Piain of Lombardy, is 27 per mille, and the maximum is 35 per mille. 
This traffic is now worked with forty electromotives, each of 60 tons weight. 
These engines have five driving-wheels connected to two eight-pole motors by 
gearwheels and rods. The pressure on each driving-axle is 12 tons. Mach 
electromotive develops 2,000 horse-power at the hour-rating; thus 1 horse-power 
is obtained for each 30 kilogramme weight of engine. 
The number of patented designs for single-phase traction motors is very 
large; but, notwithstanding considerable difference in matters of detail, all 
motors which have been successfully applied in practice may be ranged under 
three great groups—namely, the so-called repulsion type, the repulsion type with 
additional excitation of the rotor, and the straightforward series motor. The 
present tendency is rather in favour of the series motor, and the practical results 
obtained with it are certainly very promising. The latest design made by Dr. 
Behn-Eschenburg shows a remarkable weight efficiency. His 2,500 horse-power 
electromotives (the power being at a one and a half hour-rating) weigh only 
108 tons, so that at this rating 1 horse-power is obtained with a total weight of 
43 kilogrammes. ‘This compares favourably with the high-pressure C.C. system, 
where 50 to 70 kilogrammes per horse-power may be taken as normal values. 
The so-called ‘repulsion motor’ invented by Professor Elihu Thomson has 
been applied to railway work in the slightly modified form due to Mr. Deri, 
where, instead of there being only two brushes per pair of poles, double the 
number is provided, and the adjustment for speed and torque is made more 
accurate, whilst at the same time the commutation, being split up into two 
steps, becomes easier. In the matter of simplicity, an electromotive fitted with 
Deri motors cannot be surpassed by any other arrangement. There are no 
rheostats, contactors, control switches, or other gear; all the regulation is 
effected by mechanical transmission of the movement of a hand wheel placed in 
the driver’s cab to the brushes of the motors. At one time it was hoped that 
this system would win its way to a general application; but, unfortunately, the 
motor must run somewhere near synchronous speed, and becomes therefore rather 
heavy with the low frequencies alone possible in traction. | Moreover, as the 
power-factor obtainable is only about 0-80, that is, considerably below the value 
obtainable with other motors, there does not seem to be any great future for 
this system for heavy work, although its great simplicity may still turn the 
balance in its favour on lines with a light traffic. Vor heavy lines the choice 
at present lies between the induction-motor with direct rotor excitation and the 
straightforward conduction-motor, where rotor and stator are traversed in series 
by the same current. The former type of motor—also called the Latour-Winter- 
Eichberg motor—depends for its working current in the rotor on electro-magnetic 
induction, which produces the working current in the rotor much in the same 
way as the current in the secondary circuit of a transformer is produced by 
induction. Since the motor has in part the character of a transformer its 
weight would, as is the case with any transformer, be unduly augmented by 
too great a reduction in the frequency. Experience has shown that a frequency 
of twenty-five periods per second is high enough to render the transformer 
action effective, and at the same time not so high as to introduce serious 
difficulties as regards e.m.f. of self-induction and commutation. This frequency 
has been adopted in most cases where electrification of main lines has been 
carried out by motors of this class. One valuable feature of this motor is that 
at a speed slightly exceeding synchronism the power-factor may be brought up 
to unity. At this speed the commutation takes place under conditions which 
may be described as theoretically perfect. A fair number of Continental lines 
have been electrified by using these motors, and they have also been adopted, 
with very satisfactory results, in the electrification of the London, Brighton and 
South Coast lines between Victoria and London Bridge and to some distance 
1913. QQ 
