----------------------+------------+-----------+----------+---------- | | | Greatest | Least | Total |Consumption|Intensity |Intensity |Illuminating|of Gas per | of Light | of Light Description of Light. | Power. | Mile. |on Ground.|on Ground. ----------------------+------------+-----------+----------+---------- _Gas._ | candles. | cub. ft. | candles. | candles. Batswing, 7 cubic feet| 2876 | 1232 | 2·15 | 0·47 Cluster, 50 „ „ | 3857 | 1450 | 13·10 | 0·47 Siemens, 100 „ „ | 4750 | 1000 | 7·46 | 0·47 | | | | _Electricity_ | | | | Jablochkoff candle | 4408 | .. | 6·18 | 0·47 Arc light | 4750 | .. | 7·46 | 0·47 ----------------------+------------+-----------+----------+---------- It must not be lost sight of, that the illuminating power of the gas in Paris is very low, and is thus fixed. Under a pressure of 12 hundredths of an inch, gas burning at the rate of 4·05 cubic feet per hour (or 115 litres) shall give a light of 9·5 standard sperm candles (or a “Carcel” lamp burning 42 grammes of pure colza oil) per hour. The competition which has been started by the electric lighting companies has given a great impetus to gas lighting. A large number of improved street gas lamp burners and lanterns having been invented and brought into general use, the following particulars with reference to some of those which were tried in the City of Exeter may be of use as a comparison. --------------------+------------+-----------+------------------ | |Consumption| Cost per Hour, | | of gas in |gas being supplied |Candle Power| cubic feet|at 3_s._ per 1000 Description of Lamp.| of Light. | per hour. | cubic feet. --------------------+------------+-----------+------------------ | | | pence. Ordinary street lamp| 15 | 5 | ³⁄₁₆ with batswing burner| | | Siemens’ | 330 | 50 | 1³⁄₄ Ditto | 130 | 25 | ⁷⁄₈ Ditto | 45 | 10 | ³⁄₈ Sugg’s | 50 | 16 | ⁵⁄₈ Ditto | 30 | 10 | ³⁄₈ Bray’s | 80 | 20 | ³⁄₄ --------------------+------------+-----------+------------------ Having thus far given a few facts upon lighting streets with coal gas, I will now turn to the question of lighting them by means of electricity, and in doing this the following points will be considered: