THE COMSTOCK MOES. 135 



tion-wheel brought into contact with the pinion. If it be turned from the 

 drum the wheel is removed from such contact and may be held by a brake. 

 The desired motion is given to the rock-shaft, c, by the short lever, I, and the long 

 arm i, which is at the hand of the attendant. On the opposite end of each 

 drum is a rim, R, for the brake-strap. The brake is controlled by the short 

 lever yi and the arm F, which, like the arm jL, is within easy reach of the op- 

 erator. 



This method of operation has some advantages in the simplicity with 

 which the machinery is controlled and economy in the labor employed. The 

 engine runs steadily in one direction, and, not needing to be reversed, requires 

 but little attention. It may also be applied to other continuous work, such 

 as pumping, the driving of air-blowers or other machinery, which cannot be 

 done when the engine is stopped and reversed at short intervals. 



One man, in small mines or where the quantity of rock to be hoisted is not 

 very great, may attend to the whole work of controlling the engine and dis- 

 posing of the material hoisted. The attendant stands at the mouth of the mine- 

 shaft. He has, at one hand, a lever to set the winding drum in motion ; at the 

 other a lever operating the brake on the drum, and, within easy reach, the 

 means of opening or closing the throttle-valve of the engine, so that he may 

 diminish or increase the quantity of steam, according to circumstances. On 

 the arrival of the loaded car at the surface the same man may attend to its 

 discharge and send it below again. One objection to this method is, that with 

 very heavy loads the wheels are liable to slip against each other ; and another, 

 that it is not readily practicable to lower a loaded cage into the mine under 

 the control of steam, making it therefore necessary to depend entirely on the 

 brake for that purpose. This is particularly objectionable in deep mines where 

 the weight of the long cable is itself very considerable. In the Comstock 

 mines the men employed under ground are lowered into the mine on the cages ; 

 and it is always deemed safer to do this under the control of steam rather than 

 by the brake alone. 



Where cog-gearing is employed the motion of the engine is imparted to 

 the shaft carrying the winding drums or reels by toothed wheel and pinion. 

 There are various ways of applying this kind of gearing. In some cases, as 

 at the Savage, the spur-wheel and winding reel are keyed to the same shaft 



