Nov. 16, 1882] 
NATORE 
69 
“ployed by Sir William Thomson in lighting his house at 
Glasgow University. Eleven-horse power would be required to 
excite this number of incandescent lights, and at this rate the 
parish of St. James’s would require 3,018 & I1 = 33,200-horse 
power to work it. It may be fairly objected, however, that 
there are many houses in the parish much below the standard 
here referred to, but on the other hand, there are 6co of them 
with shops on the ground floor, involving larger requirements. 
Nor does this estimate provide for the large consumption of 
electric energy that would take place in lighting the eleven 
churches, eighteen club-houses, nine concert halls, three 
theatres, besides numerous hotels, restaurants, and lecture halls. 
A theatre of moderate dimensions, such as the Savoy Theatre, 
has fbeen proved by experience to require 1,200 incandescent 
lights, representing an expenditure of 133 horse power; and 
about one-half that power would have to be set aside for each of 
the other public buildings here mentioned, constituting an 
aggregate of 2,926-horse power ; nor does this general estimate 
comprise street lighting, and to light the six and a half miles of 
principal streets of the parish with electric light, would require 
per mile, thirty-five are lights of 350-candle power each, or a 
total of 227 lights. ‘This, taken at the rate of o 8-horse power 
per light, represents a further requirement of 182-horse power, 
making a total of 3,108-horse power, for purposes independent 
of house lighting, being equivalent to one-horse power per 
inhabited house, and bringing the total requirements up to 109 
lights = 12-horse power per house. 
I do not, however, agree with those who expect that gas 
lighting will be entirely superseded, but have, on the contrary, 
always maintained that the electric light, while possessing great 
and peculiar advantages for lighting our principal rooms, halls, 
warehouses, &c., owing to its brilliancy, and more particularly to 
its non-interference with the healthful condition {of the atmo- 
sphere, will leave ample room for the development of the former, 
which is susceptible of great improvement, and is likely to hold 
its own for the ordinary lighting up of our streets and 
dwellings. 
Assuming, therefore, that the bulk of domestic lighting 
remains to the gas companies, and that the electric light is intro- 
duced into private houses, only, at the rate of, say twelve 
incandescent lights per house, the parish of St. James’s would 
have to be provided with electric energy sufficient to work (9 
+ 12) 3,018 = 63,378 lights = 7,042-horse power effective ; 
this is equal to about one-fourth the total lighting power re- 
quired, taking into account that the total number of lights that 
have to be provided for a house are not all used at one and the 
same time. No allowance is made in this estimate for the 
transmission of power, which, in course of time, will form a 
very large application of electric energy; but considering that 
power will be required mostly in the. day time, when light 
is not needed, a material increase in plant will not be necessary 
for that purpose. 
In order to minimise the length and thickness of the electric 
conductor, itwould be important to establish the source of power, 
as nearly as may be, in the centre of the parish, and the position 
that suggests itself to my mind is that of Golden-square. If the 
unoccupied area of this square, representing 2,500 square yards, 
was fexcavated: to a depth of twenty-five feet, and then 
arched over so as to re-establish the present ground level, a 
suitable covered space wonld be provided for the boilers, 
engines, and dynamo-machines, without causing obstruction or 
public annoyance ; the only erection above the surface would 
be the chimney, which, if made monumental in form, 
might be placed in the centre of the square, and be combined 
with shafts tor ventilating the subterranean chamber, care being 
taken of course to avoid smoke by insuring perfect combustion 
of the fuel used. The cost of such a chamber, of engine power, 
and of dynamo-machines, capable of converting that power 
into electric energy, I*estimate at 140,000/. To this expense 
would have to be added that of providing and laying the con- 
ductors, together with the switches, current regulators, and 
arrangements for testing the insulation of the wire. 
The cost and dimensions of the conductors would depend 
upon their length, and the electromotive force to be allowed. 
The latter would no doubt be limited, by the authorities, to the 
point at which contact of the two conductors with the human 
frame would not produce injurious effects, or say to 200 volts, 
except for street lighting, for which purpose a higher tension is 
admissible. In considering the proper size of conductor to be 
used in any given installation, two principal factors have to be 
taken into account ; first, the charge for interest and deprecia- 
tion on the original cost of a unit length of the conductor ; and, 
secondly, the cost of the electrical energy lost through the resis- 
tance of a unit of length. The sum of these two, which may 
be regarded as the cost of conveyance of electricity, is clearly 
least, as Sir William Thomson pointed out some time ago, 
when the two components are equal. This, then, is the princi- 
ple on which the size of a conductor should be determined. 
From the experience of large installations, I consider that 
electricity can, roughly speaking, be produced in London at a 
cost of about one shilling per 10,000 Ampére-Volts or Watts 
(746 Watts being equal to one horse-power) for an hour. Hence, 
assuming that each set of four incandescent lamps in series 
(such as Swan’s, but for which may be substituted a smaller 
number of higher resistance and higher luminosity) requires 200 
volts electromotive force, and 60 Watts for their efficient work- 
ing, the total current required for 64,000 such lights is 19,200 
amperes, and the cost of the electric energy lost by this current 
in passing through ot-rooth of an ohm resistance, is 16/, per 
hour. 
The resi-tance of a copper bar one quartcr of a mile in 
length, and one square inch in section, is very nearly 1-100th of 
an ohm, and the weight is about 2} tons. Assuming, then, the 
price of insulated copper conductor at 9o/. per ton, and the rate of 
interest and depreciation at 7% per cent., the charge per hour 
of the above conductor, when used eight hours per day, is 14d. 
Hence, following the principle I have stated above, the proper 
size of conductor to use for an installation of the magnitude I 
have supposed, would be one of 48-29 inches section, or a round 
rod eight inches diameter. 
If the mean distance of the lamps from the station be assumed 
as 350 yards, the weight of copper used in the complete system 
of conductors would be nearly 168 tons, and its cost 15, 120/. 
To this must be added the cost of iron pipes, for carrying the con- 
ductors underground, and of testing boxes, and labour in placing 
them. Four pipes of 10 inch diameter each, would have to pro- 
ceed in different directions from the central station, each containing 
sixteen separate conductors of one inch diameter, and separately 
insulated, each of them supplying a sub-district of 1,000 lights. 
The total cost of establishing these conductors may be taken at 
37,000/,, which brings up the total expenditure for central station 
and leads to 177,000/. I assume the conductors to be placed 
underground, as I consider it quite inadmissible, both as regards 
permanency and public safety and convenience, to place them 
above ground, within the precincts of towns. With this expen- 
diture, the parish of St. James’s would be supplied with the 
electric light to the extent of about 25 per cent, of the total 
illuminating power required. To provide a larger percentage of 
electric energy would increase the cost of establishment propor- 
tionately ; and that of conductors, nearly in the square ratio of 
the increase of the district, unless the loss of energy by resist- 
ance is allowed to augment instead. 
It may surprise uninitiated persons to be told that to supply a 
single parish with electric energy necessitates copper conductors 
of a collective area equal to a rod of eight inches in diameter ; 
and how, it may be asked, will it be possible under such con- 
ditions to transmit the energy of waterfalls to distances of twenty 
or thirty miles, as has been suggested ? It must indeed be ad- 
mitted that the transmission of electric energy of such potential 
(200 volts) as is admissible in private dwellings would involve 
conductors of impracticable dimensions, and in order to transmit 
electrical energy to such distances, it is necessary to resort in the 
first place to an electric current of high tension. By increasing 
the tension from 200 to 1,200 volts the conductors may be re- 
duced to one-sixth their area, and if we are content to lose a 
larger proportion of the energy obtained cheaply from a water- 
fall, we may effect a still greater reduction. A current of such 
high potential could not be introduced into houses for lighting 
purposes, but it could be passed through the coils of a secondary 
dynamo-machine, to give motion to another primary machine, 
producing currents of low potential to be distributed for general 
consumption. Or secondary batteries may be used to effect the 
conversion of currents of high into those of low potential, which- 
ever means may be found the cheaper in first cost, in maintenance, 
and most economical of energy. It may be advisable to have 
several such relays of energy for great distances, the result of 
which would be a reduction of the size and cost of conductor at 
the expense of final effect, and the policy of the electrical engi- 
neer will, in such cases, have to be governed by the relative cost 
of the conductor, and of the power at its original source. If 
