Brass water flow measuring device in a mahogany box. The instrument comprises a detachable propeller attached to a steel shaft with a screw which drives two counting wheels which record the number of revolutions of the propeller. At the back there is a detachable rudder to ensure the propeller points upstream – this rudder is secured by a pin. Above the counting wheels at right angles to the propeller shaft there is a semi-cylindrical fitting which can be attached to a pole for use by the surveyor to insert and remove the meter from the water channel. The entire meter can be dismantled and returned to the box. This meter was used in the office of David and Charles Stevenson, CE, Edinburgh.
Mr Quentin Stevenson (donor) is a direct descendant of the Stevenson family of engineers. This item was displayed immersed in a flume as part of a conversazione held at the Museum on Monday 16 March 1998.
A manuscript note on the manufacturer’s label inside the box indicates that the meter was calibrated on 16 May 1891 to record 1.203 ft (367 mm) of water flow per revolution of the primary graduated meter wheel. The volume of water can therefore be calculated as follows: flow in cubic feet per second = 1.203 x number of revolutions x cross-sectional area (sq ft)/time period of measurement (seconds). It is noted that two previous calibrations of the instrument show flow rates of 1.367 (417 mm) and 1.427 ft (435 mm) per revolution. Clearly the accuracy of the meter was suspect being dependent on the amount of internal friction which could be affected by temperature, grit etc or even small changes in alignment resulting from knocks. The manuscript calibration notes may have been written by David Stevenson. The first calibration is dated April 1864.
For a detailed article written by David Stevenson on this flow meter click HYDROMETRICAL OBSERVATIONS“.