74 W. & L. E. GURLEY, TROY, NEW YORK 



-till water box at the surface of the water. The scale of the gage 

 bring previously set at zero with the vernier, the base is 

 fastened to the box above the water in a vertical position and 

 at such a height that the point of the hook is at the same level 

 as the crest of the weir, the precise point being secured by 

 moving the hook in the tube. The point of the hook will of. 

 course be under water and level with the crest of the weir. 



The depth of water flowing over the weir is the distance 

 between the point of the hook in the position named and the 

 exact surface of the water. To ascertain this, the hook is 

 raised by turning the milled head nut until the point of th< 

 hook, appearing a little above the surface, causes a distortion 

 in the reflection of the light from the surface of the water. A 

 slight movement of the hook in the opposite direction will cause 

 the distortion to disappear, and will indicate the surface with 

 precision. The reading of the scale will then give the depth 

 of water passing over the weir, in thousandths of a foot. 



It will be understood from the illustration that the longer 

 movements of the scale are made by loosening the large clamp 

 screw and sliding the graduated tube through the frame, the 

 finer adjustments being made by the milled nut. 



Floating gages to record only maximum and minimum 

 stages are used occasionally where such information is sufficient. 



Chain gages may sometimes be used in situations where no 

 other type could be installed. Great care should be taken to 

 secure a rigid support for a chain gage. 



All gages should be placed so that they may be easily read. 

 The scales of non-recording gages should be divided into feet 

 and tenths. When it is desirable for the ordinary gage reader 

 to read closer than tenths of a foot, the tenths should be divided 

 into halves and quarters rather than into hundredths. Exper- 

 ience has shown that the ordinary observer is able to read 

 common fractions of a tenth more readily than decimal 

 fractions. Where skilled observers are available the decimal 

 system may be used. 



