IIQ MACHINE FOR RAISING COALS OR ORE. 



Cylindrical three sides. Upon the cylindrical barrel the load always 

 tends, from gravitation, towards the nearest point of con- 

 tact with the centre of motion of the barrel, and, in conse- 

 quence, the ascending rope at first bends around it in reced- 

 ing coils from the subtending side of the rectangle, dimi- 

 nishing their distances as they approach the nearest point of 

 contact, (where the rope crosses the centres of the pulley 

 and barrel at right angles), thereby leaving a great part of 

 the latter uncovered by the rope, and hence the necessity 

 of such long ones; afterward coiling hard against itself as 

 it approaches the other side of the triangle, to its great in- 

 jury in wear. 



Conical in im- The barrels formed of frustums of cones, united at their 



proper proper- bases, the perimeters of which are in ' the proportion of 

 about five to four, are equally defective, on account of the 

 rope, for the reason before mentioned, binding hard against 

 itself, and even sometimes, (in wet weather, when its rigidity 

 is increased by absorption of water,) folding at first in re- 

 ceding coils, and afterward so hard against itself as to force 

 those receding coils to slip suddenly towards the small peri- 

 meter of the cone, thereby making a large portion of the 

 rope to descend the pit in an instant, breaking the rope by 



Danger. the sudden jerk, and frequently causing the immediate de- 



struction of the men who may be ascending the pit at the 

 time, or dashing to pieces the basket and its contents. 



Disad vantages. Beside the unnecessary expense arising from the use of 

 hempen ropes, and the breakage of chains when applied in 

 the common way, the forms of the barrels are quite erro- 

 neous in principle. Some ai*e cylindrical; others formed of 

 frustums of cones united at their bases, without any deter- 

 minate proportion in their peri-meters, or regard to the weight 

 of the rope or chain working thereon, both of which are ab- 

 solutely necessary to acquire a maximum effect. 



Proper propor- The convex surface of a frustum of a cone is equal to 



'"^"^' the convex surface of a cylinder of the same altitude, hav- 



ing its circumference equal to half the sum of the perime- 

 ters of the frustum : and circumferences of circles being to 

 one another as their diameters, the surface of a barrel 

 formed of two frustums of riglit cones (united at their 

 bases), each 64 inches diameter at one end, 32 at the other, 



and 



