THE COMSTOCK MIXES. 129 



timbers, t, t, Fig. 5, Plate IX, fixed across the shaft at right angles so as to 

 confine the rod on four sides and prevent vibration. 



The timbers, t, t, Fig. 5, which are placed in the shaft at frequent inter- 

 vals, also serve to prevent the rod from falling far, in case of fracture, by 

 furnishing support to the catching pieces, d, d, which are attached to the rod 

 for this purpose. These catching pieces are attached by iron clamps or straps, 

 which are sometimes applied as shown in Fig. 5, where each clamp embraces 

 the main rod and only one side-piece ; or sometimes, as shown in the attach- 

 ment of the plunger to the main I'od in Fig. 1, where each clamp embraces 

 the rod and both side-pieces. The arrangement in Fig. 5 is preferred by 

 some, as each side-piece is thus attached independently of the other. 



The length of stroke, or upward and downward movement of the rod, 

 varies from 3 or 4 to 7 or 8 feet, and the number of strokes per minute varies 

 from 3 or 4 to 10 or 12, according to the size and character of the pump and 

 the duty required of it. The pump-rod being continuous, where several 

 pumps are employed in a series, one above the other, as is the case in deep 

 shafts, the plungers or pistons of all the pumps so placed are attached to the 

 same rod in manner shown in Fig. 1, Plate IX. 



The weight of the rod in most cases considerably exceeds that of the 

 water to be raised, so that, descending by its own gravity, it exerts sufficient 

 force to raise the column of water without requiring additional power from 

 the engine. For the next stroke, however, the engine must lift the total 

 w^eight of the rod to the required height. 



In order to prevent the too rapid descent of the rod and to equalize the 

 work of the engine on either stroke, counter-weights are .attached to the 

 opposite end of the oscillating bob at the surface. The descending rod must 

 raise the counter-weight, which, on the reverse stroke, assists in hfting the 

 rod. In deep shafts, as the rod increases in length and weight, additional 

 counter-vv^eights are applied by establishing at various stations in the shaft 

 similar oscillating bobs, attached at one end to the rod and bearing at the 

 other end a heavily weighted box. 



Nearly all the deep-working mines on the Comstock are now supplied 

 with large pumps, similar in general character and method of arrangement to 

 such as have just been described, and varying from 10 to 14 inches in diam- 

 17 



