446 Mr. Alan A. Campiell Swinton [April 19, 



time to time as more power is required at each sub-station, and as 

 further sub-stations are inserted, all the sub-stations being in series. 



A very interesting feature is that the earth is being used as a 

 return. The earth connections are made 40 ft. down, and it is to 

 this considerable depth that must be attributed the fact that no 

 electrolysis or other inconvenience results. 



The chief advantage of the system is that, owing to its being 

 continuous current, it enables higher voltages to be used on under- 

 ground cables than would otherwise be practicable. 



As to the future, it is obvious from the lessons of the past how 

 very dangerous it is to prophesy, it being frequently the entirely un- 

 expected that turns up. So far as the immediate future of electricity 

 generation on a large scale is concerned, the steam turbine appears 

 likely to hold the field, though in regard to the smaller stations, 

 where units up to .500 or 1000 kilowatts are what are wanted, the 

 internal combustion engine is undoubtedly gaining ground. Will it, 

 however, ever catch up the steam turbine in the case of the really 

 large power stations ? As has been shown, in these, units up to 

 25,000 kilowatts are now in actual use or in contemplation, and as 

 electricity becomes more and more employed, not only for power but 

 for electro-chemical and metallurgical purposes and for domestic 

 heating, units of plant of sdll larger dimensions may be expected. At 

 present about 2000 horse-power, or about 1500 kilowatts, seems to be 

 about the maximum that is considered can be safely obtained per 

 cylinder from the internal combustion engine, so that increased 

 powers can only be obtained by a process of multiplication, which 

 leads, in the case of very large units of plant, to great complication. 

 Then again, as the steam turbine, particularly with the employment 

 of superheated steam, tends to increase in fuel economy as the dimen- 

 sions of the unit of ])lant is increased at a much greater ratio than 

 does the internal combustion engine, a point must be reached when, 

 as tlie units of plant are enlarged, taking all things, such as first cost, 

 lubricating oil, attendance and upkeep, into account, the steam turbine 

 will be as cheap or even cheaper than its rival. 



So far, the internal combustion or gas turbine has not been alluded 

 to, but some of the difficulties in the way of its successful realization 

 may be mentioned. All turbmes essentially consist of machines by 

 means of which power is obtained by the passage of fluids or hot 

 gases through narrow apertures, and by their impingement on blades, 

 in such a manner that the fluids or gases are in intimate contact 

 with large surfaces of metal. Now, as all engineers are aware, the law 

 which limits the efficiency obtainable in any heat engine is expressed 

 by the formula (T' — T)-i-T', where T' is the absolute temperature of 

 the working gas, and T the absolute temperature of the condenser or 

 the exhaust. From this it is clear that if we are to get maximum 

 efficiencies, the temperature of the working fluid must be as high as 

 possible, and the sole reason for the extra good efficiency of an internal 



