INSTRUMENTS FOR OBSERVING 23 
marks indicates the velocity of the current. The speed at which the time chart rotates 
may be regulated by the clock movement, but for general purposes a speed of one 
revolution in 6 hours is recommended. ‘This gives a time scale of 1° of are for each 
minute of time and will necessitate the changing of the chart each 6 hours. The rec- 
ord is preferably made on blank paper, and if stock charts ruled for other purposes 
are furnished, the blank side may be used for these records. The exact times of the 
beginning and end of the record must be carefully noted on each chart and interme- 
diate times, preferably each hour, should also be indicated both as a check and as a 
convenience in tabulation. 
61. The accumulator relay serves to reduce the number of electrical contacts in 
the circuit to the recorder. Each electrical contact in the current meter, representing 
FIGURE 16.—Automatic recorder for Price current meter. 
either one or five turns of the meter wheel according to whether the single-count or 
penta-count contact spring is in circuit, actuates the electro-magnet in the relay and 
moves a ratchet wheel forward one step. Interchangeable cams may be keyed to an 
extension of the ratchet wheel shaft and provide for the making and breaking of the 
circuit to the recorder after any desired number of contacts in the meter. For currents 
with velocity of less than 5 knots, a cam giving one contact in the recorder for each 10 
contacts in the meter is recommended. With this cam a recording ratio of 1:10 is 
secured when the single-count contact spring of the meter is in circuit and a recording 
ratio of 1:50 when the penta-count contact spring is in circuit. The recording ratio 
of 1:10 may be used for very weak currents, but for velocities of more than 1 knot the 
contact marks on the recording chart will tend to merge together and become indis- 
tinguishable from each other unless movement of the chart itself is also speeded up. 
For the same reason the recording ratio of 1:50 is not, in general, satisfactory for 
velocities greater than 5 knots. For larger velocities cams giving smaller recording 
