280 MAN AND NATURE. 



the more willingly accept the latter number, as it 

 comes to us justified by the very recent invention of a 

 machine for cutting coal in the mine, which not only 

 executes its work far more speedily and savingly than the 

 human arm, but, what is of far greater moment, gives 

 working access to some of those beds of coal, less than 

 three feet in thickness, which have hitherto been put 

 out of calculation, as incapable of yielding any profit. 

 As these thinner beds generally occupy areas commen- 

 surate with the thicker, the great practical value of 

 such inventions will be readily understood. 1 Concur- 

 rently with new methods for economising heat, and 

 possibly with the power of working at still greater 

 depths under the magnesian limestone, they promise to 

 retard greatly the arrival of that time certain, how- 

 ever, in the end to come when the coal-beds of Eng- 

 land will be known only as a part of its past history. 

 It is as useless to speculate on the effects of this desti- 

 tution as on the general condition of mankind at the 

 time when it shall arrive. 



Still holding to England for illustration, we pass by 

 a natural step from coal to iron that wonderful 

 metal, found now as an element in the photosphere of 



the coal resources of Great Britain, published in the ' Quarterly Journal 

 of Science' for January last. Mr. Hull adopts the larger estimate 

 noted above, and justifies it by the statistics of each separate coal-field. 



1 These coal-cutting machines, with some variations of form, have 

 now, we believe, been profitably applied in two collieries for more than 

 a year. Either steam or condensed air may be used for the engine. In 

 the former case especially It is coal working directly for its own de- 

 struction. 



We have not spoken above of the three great North American coal- 

 fields, rivalling European kingdoms in extent, as these vast deposits have 

 yet been only very partially broken in upon by the hand of man, 



