ON IMPROVEMENTS IN ELECTRIC SAFETY LAMPS. 497 



In this respect the Electric Safety Lamp has a marked advantao-e 

 over all safety lamps of the ordinary kind, which depend on the combns. 

 tion of oil ; theij cannot be made to give a mnch larger light without 

 radical alteration, if at all. If the Electric Safety Lamp is required to 

 give 5 or even 10 candle-light, it is only necessary to proportionally in- 

 crease the size and weight of the battery. Safety is not in the slightest 

 degree impaired. 



There is nothing easier than to be deceived as to the amount of light 

 that can be obtained from a certain size and kind of battery applied to 

 an incandescent lamp. If the lamp is constructed so as to allow such a 

 large current to pass through the carbon filament as will heat it to the 

 enormously high temperature at which disintegration rapidly takes place, 

 ten times as much light is produced as when, by the use of a different 

 lamp, the current is diminished, and the temperature of the filament 

 thereby lowered to a degree which will prolong the life of the lamp to an 

 economical point. 



In the case of a miner's safety lamp, it is very desirable to get as 

 much light as possible from a given weight of battery, and hence it is 

 allowable to subject the lamp filament to what may be termed a rather 

 high pressure, but not such a high pressure as will prevent the lamp 

 from lasting about 700 hours. Subject to this condition I find I can 

 obtain an average light of one standard candle during 12 hours, and 1^^ 

 candle during 9 hours, from a battery, which, with all the appurtenances 

 of the lamp attached to it, weighs altogether 5| lbs. The same battery, 

 with a different lamp filament, will, of course, give either more light 

 for a shorter time, or less light for a longer time than that I have 

 mentioned. 



The battery cells are slightly different in construction from those in 

 last year's lamp. They consist, as before, of a central solid cylinder of 

 peroxide of lead, with a conducting core of lead wire, fixed concentrically, 

 by means of guide rings of india-rubber, within a tube of lead, the in- 

 ternal surface of which is in the spongy state. The annular space 

 between the peroxide of lead cylinder and the lead tube is filled with 

 dilute sulphuric acid. Four such elements are fitted into four ebonite 

 lined holes in a block of wood saturated with paraffin. The lead wire 

 connections between cell and cell are covered with india-rubber, and 

 embedded in channels in the wood, and covered with Chatterton's com- 

 pound. Over the buried connecting wires is fixed a veneer of ebonite, 

 which further protects them, and also forms a level seat for the cushion 

 of india-rubber, which, when pressed down by the cover-disc makes the 

 cells liquid-tight, so that the whole block may be laid on its side, or in- 

 verted, without leakage. 



In the form of lamp I showed last year the cover of the case which 

 contained the battery had to be screwed off to get at the battery 

 terminals, for the purpose of putting them in connection with the charg- 

 ing circuit. In the new design the removal of the cover is avoided by 

 bringing down the battery terminals to the bottom. Access is given to 

 these through two small holes, within which fit two pins connected with 

 the positive and negative charging wires. Charging is effected by simply 

 placing the lamp on a bench fitted with charging pins, in connection 

 with wires from a dynamo, so that the charging pins enter the two holes 

 at the bottom of the lamp case. The lamps remain on the dynamo cir- 

 cuit, receiving their charge during the time the men who have used the 

 1886. K K 



