210 Mr. William Henry Preece [Feb. 10, 



to be extinguished in handling like the Mueseler ; but they do not 

 act as detector of the presence of gas, and they might explode gas if 

 their protecting glass shield were accidentally broken. 



It is remarkable that Davy himself in 1815 experimented with an 

 arc lamp in a closed vessel of glass, but it was not until 1865 that a 

 practical lamp was proposed for collieries. Dumas and Benoit used 

 a small Geissler tube illuminated by sparks from an induction coil 

 and excited by a primary battery ; but it was heavy — it was a kind 

 of knaj^sack to be carried on the back, and it met with no success. 



Mr. Swan has been more successful. The great success of the 

 glow lamp, in the introduction of which he has played so prominent 

 a part, and the perfection of the secondary battery have enabled him 

 to produce a lamp that compares in weight and size and light with 

 the best mechanical lamp. Eight hundred of these lamps are in 

 constant use in the National Colliery in the Ehondda Valley in 

 South Wales, and 1600 more are on order for the Kisca and Aber- 

 carne Collieries belonging to Messrs. Watts, Ward, and Co. They 

 are giving great satisfaction. A collier told me that the electric 

 light was " as good as the moon." The lamp batteries are charged 

 a great number at a time in blocks at the pit bank. 



Mr. Pitkin has also been very successful in making light portable 

 lamps, and they have been practically used in Cannock Chase and at 

 the Tyldesley Collieries in Lancashire. 



The " Sun " lamp is another very promising form, worked by 

 secondary battery. It is light — 3 lb. 12 oz. ; it gives IJ candle, and 

 this is maintained for ten hours. Secondary cells usually require 

 about twelve hours' charge to emit a ten hour discharge, but this cell 

 will give a ten-hour discharge with four hours' charge. It is fitted 

 with a safety appliance — a plan patented by Mr. Senuett in 1882 — 

 by which the lamp is automatically switched out the instant that the 

 outer protecting glass is broken or cracked, so that contact between 

 the hot filament of the lamp and the explosive gas is prevented. 

 This safety appliance has been tested by Mr. Hhodes at the Aldwarcke 

 Colliery in actual explosive mixtures. 



Many efi"orts have been made to introduce primary batteries for 

 the same purpose, but up to the present moment I have seen only 

 one — the Schanschieff — which, in efiiciency, lightness, and economy 

 comes up to the requirements of a safety lamp. A primary has this 

 advantage over a secondary battery — that it is charged at once by an 

 operation as simple as that of trimming a Davy. To trim a Davy 

 means thorough cleaning, inserting a fresh wick, pouring in new 

 oil. A primary battery means pouring out old, and pouring in fresh 

 solution. 



Occasionally zincs require renewal, but all these operations are 

 within the intelligence of the collier, and the lamps need not go to 

 the surface. The simplicity of the operation has distinct merits of 

 its own that compensate for the extra cost of the materials used. 



The chief charm of the electric lamp is not the greater light that 



