92 LIGHT SCIENCE FOR LEISURE HOURS. 



aspect. Of the stores which the Commissioners regard 

 as available a vast proportion must be mined out from 

 depths far exceeding any which have been at present 

 reached in England. It is not as yet clear how far the 

 increase of depth will add to the cost and risk of 

 working ; nor do I propose to discuss a subject which 

 can only be adequately dealt with by those who possess 

 practical knowledge of the details of colliery-working. 

 I will content myself by quoting some remarks on the 

 subject, in an inaugural address delivered by Mr. 

 G-eorge Elliot (one of the Koyal Commissioners) before 

 the North of England Institute of Mining Engineers 

 in 1868. ' The great depth,' he remarked, ' at which 

 many of our pits are worked, and the vast extent of 

 their lateral ramifications, make it more than ever 

 necessary that we should secure the best mode of 

 rendering the supply of pure air certain, regular, and 

 safe. It is maintained that ventilating by machinery 

 ensures these desiderata ; that the nicety with which 

 mechanical appliances may be regulated, the delicate 

 adjustment of power of which they are capable, and the 

 complete safety with which they may be worked, place 

 them far before the system they are intended to super- 

 sede. The extent of our coal supply will be materially 

 increased by the improvement of which this is a 

 type. ... It is probable that the ordinary means 

 of ventilation whether by furnace or fan may be 

 aided by a change in the force or agency employed for 

 the purposes of haulage and other independent work. 

 As an instance of my meaning, I may mention that the 



