DBA~ SzR :--In answer to your letter, inquiring the actual relation which the water passing Fairmount Dam bears to the rain-fall upon the entire drainage area, and the further utilization of the water power of the river, I would state that the relation existing between the rain-fall on the Schuylkill basin, and the water discharged at Fairmount, has never been definitely determined.
Prior to my retirement from the management of the water department, considerable preliminary work had been done, and a plan had been matured for a thorough investigation of the hydrography of the Schuylkill Valley, which would have given accurate data for ascer-t~fining all the characteristics of the stream and its basin. The work accomplished may be briefly summarized as follows :
"A." The records of rain-fall upon the area drained, which were made by various observers, were collected and tabulated. Rain gauges were located in places where none had bee~ placed before, and which were necessary to the proper examination of the subject. "B." A gauge was constructed with a vernier reading to the thousandth part of a foot, and located beyond the influence of the Fairmount Water Works, so as to measure the flow of water over the comb of the dam. Frequent readings of this gauge were taken.
For a number of years, measurements had been made, and records kept of the flow of water over the dam, but they were unreliable because they were taken from a cast iron gauge, permanently secured to the masonry of the gate bridge, possessing the following defects : 1st. The zero point did not coincide with the level of the dam. 2d. The markings were only in inches, and these were incorrectly spaced. 3d. It was so located that an observer could not get close enough to it for accurate reading. 4th. Being situated in the fore-bay, the gauge was influenced by the operation, starting or stopping of the wheels. 5th. The readings had been taken but twice in a day.
"U." The flow of water over the dam was found to be influenced by the operation of the wheels of the water works, and of the factories at the Falls and Manayunk, and also by the lockage of boats, and the direction and intensity of the wind. It was, therefore, evident that no record but a continuous one would represent the daily average, and to secure such a record, an automatic recording gauge,