224 SCIENCE IN SHORT CHAPTEE3. 



which depend upon abundance of cheap coal, such as the manufact- 

 ure of pig-iron, etc.* 



The action of increasing prices has been but lightly considered 

 hitherto, though its importance is paramount in determining the 

 limits of our coal supply ; I even venture so far as to affirm that it is 

 not the depth of the coal seams, not the increasing temperature nor 

 pressure as we proceed downward, nor even thinness of seam, that 

 will practically determine the limits of British coal-getting, but 

 simply the price per ton at the pit's mouth. 



In proof of this, I may appeal to actual practice. Mr. Hull and 

 others have estimated the working limit of thinness at two feet, and 

 agree in regarding thinner seams than this as unworkable. This is 

 unquestionably correct so long as the getting is effected in the usual 

 manner. A collier cannot lie down and hew a much thinner seam 

 than this, if he works as colliers work at present. But the lead and 

 copper miners succeed in working far thinner lodes, even down to 

 the thickness of a few inches, and the gold-digger crushes the hardest 

 component of the earth's crust to obtain barely visible grains of the 

 precious metal. This extension of effort is entirely determined by 

 market value. At a sufficiently high price the two-feet limit of coal- 

 getting would vanish, and the collier would work after the manner of 

 the lead-miner. 



We may safely apply the same reasoning to the limits of depth. 

 The 4000-feet limit of the Royal Commissioners is at present unattain- 

 able, simply because the immediately prospective price of coal would 

 not cover the cost of such deep sinking and working ; but as prices 

 go up, pits will go down, deeper and deeper still. 



The obstacles which are assumed to determine the 4000-feet limit 

 are increasing density due to greater pressure, and the elevation of 

 temperature which proceeds as we go downward. The first of these 

 difficulties has, I suspect, been very much overstated, if not alto- 

 gether misunderstood ; though it is but fair to add that Mr. Hull, 

 who most prominently dwells upon it, does so with all just and 

 philosophic caution. He says that " it is impossible to speak with 

 certainty of the effect of the accumulative weight of 3000 or 4000 feet 

 of strata on mining operations. In all probability one effect would 

 be to increase the density of the coal itself, and of its accompanying 

 strata, so as to increase the difficulty of excavating," and he con- 

 cludes by stating that " in the face of these two obstacles tempera- 

 ture and pressure, ever increasing with the depth I have considered 

 it Utopian to include in calculations having reference to coal supply 

 any quantity, however considerable, which lies at a greater depth 

 than 4000 feet. Beyond that depth I do not believe that it will be 

 found practicable to penetrate. Nature rises up, and presents insur- 

 mountable barriers." f 



On one point I differ entirely from Mr. Hull, viz. the conclusion 

 that the increased " density of the coal itself and of its accompany- 

 ing strata" will offer any serious obstacle. On the contrary, there is 



* At the present time (1882) we are receiving the excessive supplies consequent 

 upon the opening of new pits that, under the Ptimnlus of high prices, were in the 

 course of sinkinsr when the above was written. Hence the present low prices. 

 Presently the annual increase of consumption will overtake this increased supply, 

 and another "coal famine" like that then existing will follow. This is not far 

 distant. 



t " The Coal Fields of Great Britain," pp. 447, 448.' 



