128 THE SCIENTIFIC PAPERS OF 



In the discussion of the Papers 



"ON MACHINES EMPLOYED IN WORKING AND 

 BREAKING DOWN COAL, so AS TO AVOID THE USE 

 OF GUNPOWDEE," by SAMUEL PAEKEE BIDDEE, Jun. Assoc. 

 Inst. C.E. ; and 



"ON COAL GETTING MACHINERY, AS A SUBSTITUTE 



FOE THE USE OF GUNPOWDEE," by CHAELES JOHN CHUBB, 



ME. C. W. SIEMENS*" remarked that it was of the greatest 

 interest to all that coal should not only be got economically, but 

 without involving human suffering. Although it had been as- 

 serted that the casualties caused by the explosion of powder were 

 not so numerous as might have been supposed, nevertheless it was 

 acknowledged that there was a serious loss of life every year. 

 Independently, however, of that, there was the question of annoy- 

 ance and injury to health that might be produced by noxious 

 vapours arising from the explosion of powder in confined spaces. 

 Moreover, it had been shown that coal could be got more 

 economically by wedging than by blasting. The quantity of coal 

 released by wedge action must be greater than that released by 

 explosions, inasmuch as powder threw out the cone of least 

 resistance, whereas a wedge would exert its power upon a larger 

 range of coal. The question of undercutting the coal was no 

 doubt important. He had been endeavouring to calculate what 

 force would be expended in each case, but he had not been able to 

 obtain a satisfactory result. If the coal was holed, or undercut, a 

 disc of it had to be dealt with, and with the wedge the line of 

 cleavage would be contained in that disc. He expected that the 

 force expended would increase with the depth at which the force 

 was applied ; so that if the machine was inserted into a hole 4 feet 

 deep, it would expend four times the force that it would if the 

 machine was put in only 2 feet deep. But the question became 

 much involved if the coal was to be torn out of the face, because 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, Vol. 

 XXVIII. Session 1868-1869, pp. 141-142. 



