As to the value of the electric light, there can be no doubt that a most brilliant and powerful light is produced by the voltaic arc: so brilliant indeed, as to render it necessary to screen it nearly always behind frosted or opalescent glass globes, the former being found to be much the best for many reasons.

As to the photometrical value of the light, some considerable difficulty has hitherto been experienced in obtaining accurate observations, principally owing to the peculiar colour of the electric light, and also from its fluctuating character; but these difficulties are being steadily overcome, and with a photometer mounted on a light frame with wheels, some excellent experiments have been made in the public streets upon the comparative values of different lights.

(4.) The last and really one of the most important questions remaining to be discussed is that of the cost of the electric light as compared with gas.

With reference to the cost of the electric light, the following table may be of use; it is compiled from an excellent paper on electric lighting, by Mr. James N. Shoolbred:[118]

Table of Comparative Estimates of First Outlay and
of Working Expenses of some Systems of Electric Lighting.

Name of Machine.First Cost, including
Engine to drive it.		Working Expenses per hour.
One
light.		Two
lights.		Three
lights.		Five
lights.		One
light.		Two
lights.		Three
lights.		Five
lights.
££££s.d.s.d.s.d.s.d.
Gramme single light “A” with Siemens lamp -33053572593516 21 27 30
Cost per light per hour -————111·414·812·2010·2
Siemens single light “medium” with Siemens small-sized lamp -365611835118517¹⁄₂[119]24 210 39
Cost per light per hour -————21·416·813·8410·8
Six
lights.		Twenty
lights.		Six lights.Twenty lights.
££ s.d. s.d.
Gramme “many light” machine with candles -5761155 28 63
Cost per light per hour -—— 06·4 04·2

Mr. Shoolbred has also given another table[120] of street lighting which partly deals with the question of cost, it is as follows:

Date of
Lighting.		Cost to
Municipal
Authority.		Length of
Street Lit.		Annual
Cost
per mile
of street.		No. of
Lamps.		Illuminating
Power
of each
(on
horizontal).		Remarks.
City of London.
District No. 1. (Ludgate Hill, &c.).—“Brush” Electric Light Co.
£yards
lineal.		£ candles.
Mar. 31, 1881
to
Mar. 30, 1882		 -660[[A]]175066032 arc9501 40-light Brush machine.
[A] Add £750 to cost, for fixing and final removal of apparatus.
District No. 2. (King William Street, &c.).—Siemens Bros. & Co., Ld.
Mar. 31, 1881
to
Mar. 30, 1882		 -2270[[B]]196020266 arc40006 continuous current machines.
23 arc3302 alternating ditto.
[B] Add £1450 to cost, for fixing and removal of apparatus.
Metropolitan Board of Works (Thames Embankment).—“Jablochkoff” Co.
Dec. 13, 1878
to
June 30, 1881		 -2¹⁄₂d. per light per hour.2540113160 candles3803 Gramme double-machine (“A” and divider).
1 Ransome’s steam engine. 20 HP nominal.
July 1, 1881
to
June 30, 1884}		 -1¹⁄₂d. per light per hour...753
City of Norwich (Prince of Wales’ Road,&c.).—R. E. Crompton & Co.
Aug. 15, 1881
to
Jan. 31, 1883		 -71017005315 arc20004 Bürgin machines.
9 arc5001 Ransome’s steam engine, 20 HP nominal.
Chesterfield (Market Place, &c.).—Brush (Hammond) Electric Light Co.
Nov. 1, 1881
to
Oct. 31, 1882		 -8553500..22 arc9502 40-Light “Brush” machines.
100
Incan-
descent.		162 Fowler’s semi-portable compound engines 20 HP nominal.

As to the comparison of cost between the electric light and gas, this has only, I believe, been properly estimated on the Thames Embankment, London, by Sir Joseph Bazalgette, the results of whose investigations upon this important point I shall give [presently]; it has, however, been stated generally, and without contradiction, that arc lights can be produced of about 2000 candle power, with 1 HP at a cost of from 3d. to 6d. per candle per annum of 4000 hours, gas costing from 1s. 9d. to 3s. 6d. per candle according to the price of the gas.

Incandescent lamps cost 3s. to 4s. per candle per annum, as their life is short, and only 200 candle power can be got from 1 HP.[121]