The following table will show the particulars of different lights so placed that persons may see to read ordinary print in any part of the street, which may be taken as then being a well-lighted street.
| Description of Light. | Illumi- nating Power. | Height of Lamps. | Distance of Lamps apart. | Number of Lamps per Mile. | Total Illumi- nating Power. | Con- sump- tion of Gas per Mile. | Greatest Intensity of Light on Ground. | Least Intensity of Light on Ground. | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Gas. | candles. | ft. | in. | yards. | candles. | cub. ft. | candles. | candles. | ||||
| Batswing, | 7 | cubic | feet | 16·34 | 9 | 10 | 20 | 176 | 2876 | 1232 | 2·15 | 0·47 |
| Cluster, | 50 | „ | „ | 133·00 | 10 | 6 | 115 | 29 | 3857 | 1450 | 13·10 | 0·47 |
| Siemens, | 100 | „ | „ | 475·00 | 26 | 3 | 294 | 10 | 4750 | 1000 | 7·46 | 0·47 |
| Electricity | ||||||||||||
| Jablochkoff candle | 152·00 | 16 | 3 | 120 | 29 | 4408 | .. | 6·18 | 0·47 | |||
| Arc light | 475·00 | 26 | 3 | 294 | 10 | 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.
| Description of Lamp. | Candle Power of Light. | Con- sumption of gas in cubic feet per hour. | Cost per Hour, gas being supplied at 3s. per 1000 cubic feet. | |
|---|---|---|---|---|
| pence. | ||||
| Ordinary street lamp with batswing burner | 15 | 5 | ³⁄₁₆ | |
| Siemens’ | 330 | 50 | 1 | ³⁄₄ |
| 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:
(1.) The motive-power to be employed in producing electricity and its applicability for the purpose.
(2.) The description of machinery to be employed.
(3.) The value of the light produced, and its adaptability to the requirements of any town.
(4.) The comparative cost of the electric light as compared with gas.