16 BULLETIN 376, U. S. DEPARTMENT OF AGRICULTURE. 



on pipes up to 6 feet in diameter were abstracted, but no other tlian 

 the writer's records are available for pipes between 6 and 12 feet in 

 diameter. 



EQUIPMENT AND METHODS EMPLOYED FOR COLLECTING AND INTER- 

 PRETING FIELD DATA. 



In order to correctly weigh any new data bearing on hydraulic 

 formulas it is necessary to know in detail the equipment used and the 

 steps pursued in both the field and office. Consequently these 

 features are described in some detail. 



EQUIPMENT. 



Tapes. — ^High-grade steel tapes, graduated in feet and hundredths, 

 were used in the determination of diameters, circumferences, etc. 

 For distance chaining the tape was graduated to tenths. 



Level. — ^An 18-inch Berger engineer's wye level, equipped with a 

 bubble whose sensibility was rated at 10 seconds of arc for 1 division 

 of scale equal to one-tenth of an inch was used. The bubble vial was 

 6.5 inches long; the telescope power was 35 diameters. The instru- 

 ment was kept in excellent adjustment. 



With oae exception the levels in these tests were closed within the 

 limits suggested by the U. S. Geological Survey, the allowable error 

 in feet being 0.017 Vdistance in miles.^ The exception noted occurred 

 in connection with the tests on pipe No. 37, where the levels were run 

 in high wind, over deep sand. Several trials were made, but the best 

 closure was to 0.023 foot, while to conform to the formula it should 

 have been to 0.012 foot, the distance being about 2,500 feet. 



Rod. — ^A new Philadelphia rod, in three sections, equipped with rod 

 level and vernier reading to thousandths of a foot was used in the 

 determination of the elevations of gauge zeros with regard to an 

 assumed datum. 



Thermometers. — ^Temperatures of air and water were taken with 

 all-glass laboratory thermometers, graduated to degrees and fifths. 

 Centigrade scale. The range covered in the graduations was only 

 that liable to be encountered in the tests, so that each degree was 

 represented by about three-sixteenths inch. 



Hydrometer. — Specific gravity of water in the pipes was tested by 

 means of a laboratory hydrometer simultaneously with a like deter- 

 mination of the temperature of the water. The hydrometer was 

 afterwards tested by the U. S. Bureau of Standards. The proper 

 corrections were thereafter applied to readings before computation was 

 undertaken. 



Current meter. — ^A small Price cup current meter of the combina- 

 tion type was used. This meter had been carefully rated by the U. S. 



» Precise Leveling, in Topographic Instructions of the U. S. Geological Survey, 1913, p. 100. 



