158 IRRIGATION FARMING. 



Stopped and the second reading is made, and these, 

 together with the time, noted down. The difference 

 between the first and second reading is divided by the 

 time, which gives the revolutions per second. The 

 revolutions per second multiplied by the ratio will give 

 the velocity of the stream in feet per second. In the 

 computations the following formula is used : Total 

 number of revolutions divided by the time equals the 

 revolutions per second. Total distance divided by the 

 time equals the velocity in feet per second which the 

 meter moves through the water. Velocity in feet per 

 second divided by the number of revolutions per second 

 equals the ratio. 



The Water Register. — This is a device used in 

 measuring the water that flows in specified currents, 

 such as rivers, canals, or flumes. Fig. 44 gives a very 

 good idea of its mechanism. 



It consists of a dial divided circumferentially into 

 spaces corresponding to the days of the week and the 

 hours and minutes of the day. Beginning at the cir- 

 cumference and going toward the center of the dial it 

 is divided into a scale of feet and inches. The dial is 

 turned by clockwork, making one revolution in seven 

 days. Pressing against the dial is a pen filled with a 

 specially prepared ink which does not dry in the pen. 

 This pen is one of two arms attached to a revolvable 

 shaft, the other arm being in the form of a segment of 

 a gear. This segment meshes with a small pinion 

 secured to a shaft carrying a grooved pulley. Over 

 the grooved pulley a cord is passed, carrying at one 

 end a float which rests upon the water to be measured 

 and at the other end a weight which nearly counter- 



