498 REPOET~1886. 



lamps are resting, and they become fully charged by the time these men 

 return to work. 



It is a point in favour of this kind of lamp that the operation of re- 

 newing the charge is effected with little trouble and cost — far less than 

 is involved in replenishing and cleaning ordinary safety lamps. For 

 example : one horse power is sufficient to charge one hundred lamps at a 

 time; that item of cost will, therefore, not exceed a farthing a lamp per 

 week. 



The total cost will not exceed fivepence per week, where several hun- 

 dred lamps are in constant use. That amount will, I estimate, cover the 

 total weekly cost per lamp, including renewal of lamp-bulbs, the cost of 

 fuel, wages for keeping the lamps charged and in repair, and interest at 

 ten per cent, on the capital outlay for the whole plant, including the lamps 

 themselves. 



In one of the modifications of the lamp the light is fixed upon the top 

 of the case, with a view to the illumination of the roof and sides of the 

 mine. 



This form of lamp is intended for the use of over-men while travelling 

 in the workings. 



The bull's-eye form, with the light on one side, is intended for the use 

 of the hewer. While the hewer is at work the lamp will be hung up on 

 a hook as usual. 



"Where low workings have to be traversed the lamps can be fastened 

 to the breast of the miner by a strap across the shoulder. 



The only other point requiring explanation is the fire-damp indicator. 

 The want in the lamp I showed last year, of the means of showing the 

 presence of fire-damp, was urged as an objection to it. I have met the 

 objection by adding an indicator. This will not be required on every 

 lamp, but only on lamps used by over-men. I have made the indicator in 

 three forms ; two of these act on the same principle as Liveing's fire- 

 damp indicator. A spiral coil of thin platinum wire is arranged so that 

 it can be heated to a low red heat by switching through it the current 

 generated by the lamp battery. If this takes place in an atmosphere in 

 which fire-damp is present, the wire becomes hotter than when heated in 

 pure atmospheric air, because combustion of the fire-damp with the 

 oxygen of the air, brought about by the electrically heated wire, produces 

 additional heat, and, consequentlj^, increases the temperature of the wire, 

 so that it is sensibly brighter whan heated in air containing fire-damp 

 than when heated in air in which there is no fire-damp. 



In one form of the indicator I have followed Mr. laveing's idea of 

 having a comparison wire, shut up, air-tight, in a glass tube containing 

 pure air. In another I have deviated from Liveing's construction in two 

 ways ; namely, by having only one wire (the test wire), and instead of 

 this being in a wire gauze cage, always exposed to the atmosphere in 

 which the lamp is placed, it is in a tube which, when the current is 

 turned on to heat the wire, is completely closed. It is not easily con- 

 ceivable, even if the test were made in an atmosphere of air and fire-damp 

 of maximum explosiveness, that flame would pass the fourfold lining of 

 fine copper wire gauze of the Liveing indicator ; still it is, perhaps, more 

 consistent with the absolute safety of the lamp itself to make the test in 

 a closed vessel. With the double wire arrangement, when fire-damp is 

 present in the air, even in so small a proportion as half a per cent., the 

 exposed wire glows with perceptibly greater brightness than the enclosed 



