LAMBTON B. COLLIERY. 



315 



but there is no occasion to have it wide, since the air can 

 escape all round its circumference. The trumpet-shaped out- 

 let extending beyond the ends of the blade increases the ef- 

 ficiency of the fan, since less power is required to discharge 

 the air, for the area of the outlet being greater than that at 

 the tips of the blades, the velocity of discharge is gradually 

 reduced, and resistance" varies with the square of the velocity. 

 It is better not to have a bearing on the intake side of the 

 fan, as it stops the free inlet of air. A Waddle fan can be 

 worked at a greater rate than a Walker fan, as the latter, if 

 driven too fast, would shake about and wear out the bearings. 

 There are two loose doors on the top of the air shaft, which 



Fig. 202. Jeffrey Conveyor. 



act as a safeguard in case of an explosion, in addition to the 

 windows, which would naturally break. A large grating is 

 placed in front of the fan in the fan drift. 



Cambrian safety lamps, an improvement on the Evan 

 Thomas lamp, are used at this colliery. The lamp cabin, with 

 the necessary appliances for cleaning, filling and locking the 

 lamp is shown in Fig. 201. When ready for use the lamps are 

 placed on four decker turn tables. The upper portion of each 

 lamp is suspended from a numbered hook above its corres- 

 ponding oil vessel, so that the wick can be readily lighted 



