120 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
point of the dome of water above, in a strictly vertical direction
--a to b in the diagram. Then these distances may be found in the table and the corresponding figure will give the number of gallons discharged per minute. The blowing of the wind need not interfere in this case as long as the measurements are taken vertically.
"The method for determining the discharge of horizontal pipes requires a little more care. First, measure the diameter of the pipe as before, then the vertical distance from the middle of the opening of the pipe, or some convenient point corresponding to it on the side of the pipe, vertically downward six inches-a to b, then from this point strictly horizontally to the center of 'the streamb to e. With these, data, the flow in gallons per minute may be obtained from the table. It will be readily seen that a slight error may make much difference in the discharge. Care must be taken to measure horizontally and also to the middle of the stream.
"Because of this difficulty, it is desirable to check the first determination by a second. For this purpose, columns are given in the tables for corresponding measurements twelve inches below the centre of the pipe. Of course, the discharge from the same pipe must be the same in measurements of the same stream. In this case, the occurrence of wind, blowing either with or against the water, may vitiate results to an indefinite amount, therefore measurements should be taken while the air is still.
"The flow of pipes of diameters not given in the Table II., may be easily obtained for corresponding *measurements, as follows: For Y2 inch, multiply discharge of i-inch pipe by .25; for 34-inch, by .56; for i'4-inch, by 1.56; for iy2-inch, by 2.25. For 3-inch, multiply 2-inch pipe by 2.25; for 4-inch, by 4; for 5-inch by 6.25; for 6-inch, by 9; for 8-inch by 16.
"In both these tables it has not been thought necessary to make any allowance for the resistance of the atmosphere. Doubtless when the velocity of the stream is great, the resistance is considerable; but as the pressure checks the flow, and our object is simply to measure the amount of flow, it need not be taken into consideration. In case pipes are found of diameters not corresponding to the table, the same rule may be applied as in the first case.
"Whenever fractions occur in the height or horizontal distance of the stream, the number of gallons may be obtained by dividing the difference between the readings in the 'table for the nearest whole numbers, according to the size of the fraction. For example, if the distance from the top of the pipe to the top of the stream, in