POWER DISTRIBUTION IN THE LABORATORY. 267 



from the supply in the street. A adjustable pulley for regulating the 

 tension of the cord. The wheel is set to run at one revolution a 

 second for ordinary class purposes, and is geared to the shaft S by 

 means of a cord which connects the reducing pulley R to the driving 

 pulley P. The cord is guided in the required change of direction by a 

 system of guide pulleys D, shown in side view in the right-hand figure. 

 By means of these the cord is also taken to the counterpoise C, which 

 maintains an equable tension. Cord r to cone R on the wheel; W 

 marks the position of the latter in section. 



The shaft S is of 1-inch steel tubing, carried on Bown's ball 

 bearings at intervals of 30 inches. Upon it speed cones P' are 

 threaded, one for each recording drum in the laboratory. 



Each speed cone is 15 inches in diameter, and is built up of 

 mahogany. It turns once in 1J seconds when W is making one turn a 

 second. The cord connection to a drum is shown in Fig. 34 I, where 

 the tension pulley L and guide K, immediately over each work table, 

 are also seen. 



As all the rolling parts are either borne upon centres U (a pulley 

 shown in section), or in ball bearings, friction is reduced to a minimum; 

 and as, furthermore, the wheel is loaded with lead L, and the cylinder 

 cones on the tables are heavy (Fig. 34 D), these together form a system 

 of fly wheels which produce great steadiness of running. 



With a water pressure of 25 pounds at the motor, a very constant 

 rate of movement is obtained, which is not appreciably affected by 

 starting and stopping the drums. 



Under a fortieth of a horse power is required to drive the whole 

 apparatus in the laboratory. 



The speed of W is ascertained by counting its revolutions by a 

 watch, for which purpose a white mark X serves as a guide. 



The wheel is fixed to the wall by a three-branched bracket, seen 

 behind R, and is mounted upon it in the same way as the pedal of 

 a bicycle on its crank. 



Simplicity and economy in working are salient features of this 

 arrangement. 



