Chemical Change and Energy 343 



FIG. 179. The explosion of 75 pounds of dynamite. A "still" from a motion- 

 picture film. 



engines for pumping water or running machinery would 

 not be of any use ; and all aviation would immediately 

 cease. Tunneling through mountains, building roads in 

 rocky places, taking up tree stumps, and preparing hard 

 ground for crops would all be made very much more 

 difficult. War would have to be carried on much as 

 it was during the Middle Ages; soldiers would use 

 spears and bows and arrows ; battleships would be 

 almost useless in attacking; modern forts would be of 

 little value; cannon, guns, rifles, howitzers,- mortars, and 

 revolvers would all be so much junk. 



