400 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



machine employed to supply the power. The heat of the 

 electric arc is sufficient to vaporize the insulating material 

 employed between the carbons, as these are consumed, and 

 thus their relative distances are preserved. The alternation 

 of the current provides for any unequal consumption of the 

 carbons. The candle may be used in any position. It ad- 

 mits of being lighted at a distance by placing previously a 

 piece of pencil-lead between the carbons, which allows the 

 current to pass at first, but gradually consumes, after which 

 the brilliant arc appears. The gradual fusion, also, of the 

 insulating material increases the length and intensity of the 

 light produced. It has been suggested, likewise, that the 

 candle might be employed for transmitting signals by flash- 

 es, inasmuch as it may be repeatedly relighted after being 

 extinguished by the breaking of the circuit, provided the 

 interval be not too long. This invention has undoubtedly 

 carried us a decided step forward towards proving the en- 

 tire practicability of the electric light for general lighting 

 purposes. The cost of operating is said to be considerably 

 lower than that of coal-gas, experiments at the West India 

 Docks, London, having afforded the ratio of 30 to 100, show- 

 ing a saving, estimated on an equivalent quantity of light 

 supplied by both methods, of 10 per cent, in favor of the 

 electric light. 



We may also mention, in this connection, the fact that an 

 electro-magnetic machine designed by Loutin, and by which 

 a number of independent currents of different strengths are 

 generated and distributed to separate circuits to feed a 

 separate light in each, has been tried with much success in 

 France. 



In connection with light-house illumination, the compara- 

 tive trials of the magneto -electric machines of Siemens, 

 Gramme, and Holmes at the South Foreland Light-house, 

 made under the direction of Professor Tyndall, are worthy 

 of notice. These trials appear to have established the su- 

 periority of the Siemens machine. 



UTILIZATION OF BLAST-FURNACE SLAG. 



It is worthy of remark that during the past year the sub- 

 ject of turning this waste product of the iron-manufacture 

 to good account has attracted a considerable share of atten- 



