produced by a Fluid in Motion. 213 



subsequently devised the apparatus of which the following is 

 a description. 



A, Plate III. fig. 1, is a conical glass vessel closed above 

 and below by corks ; through the upper cork passes a glass 

 tube B, 24 inches long and f-Jths of an inch internal diameter ; 

 3 inches of B are within the vessel A, and a scale of inches is 

 attached to that part of B outside A ; a tube C, -^-ths of an inch 

 diameter, communicating with the interior of A, is bent twice at 

 right angles, and passes into a circular glass vessel D, which 

 has a scale of inches attached to it, and is provided with a stop- 

 cock E. A tube F of small diameter communicates with the 

 interior of A both above and below ; a scale is attached to it, 

 and by it the absolute level of water in A is shown ; through 

 the lower cork of A passes a stopcock G. II is a glass tube 

 communicating with the water-cistern by means of a caoutchouc 

 tube, 1 1 1 ; a similar caoutchouc tube, K K, is connected with the 

 stopcock G, and the two tubes are brought together and can be 

 closed or opened simultaneously by the spring clip L. A half- 

 litre flask, M, collects the air which is carried down by the 

 descending stream. The dotted lines a, b, c, d, e show the dif- 

 ferent levels at which water was caused to remain constant in A 

 during separate experiments. 



The water-cistern was about 8 feet from the apparatus, and 

 the water within it was kept at a constant level of 2 feet above 

 the orifice of the delivery-tube H. The caoutchouc tube, III, 

 was of such diameter that it delivered half a litre of water in 16 

 seconds at the height of the tube H. 



In order to prepare the apparatus for an experiment, water 

 is placed in the vessels A and D to the level required in each ; 

 the flow from H is determined, and the orifice of H is then 

 brought on a level with that of the tube B, and so placed that 

 when water is flowing, it passes exactly down the axis of B. 

 The efflux from H remaining constant, the efflux from A is 

 made equal to it ; this is done by keeping the eye on the scale of 

 F and turning the stopcock G until the water-column in F 

 remains perfectly immoveable at the desired level; the caout- 

 chouc tubes III and K K are then brought together at one 

 point, and are closed by the spring clip L ; finally, the half-litre 

 flask M is filled with water, and inverted over the orifice of the 

 tube C. A watch, suspended behind a large lens, is placed in 

 such a position that the eye can observe both it and the level of 

 water in D with as little difficulty as possible. Immediately 

 before an experiment, the spring clip L is removed from the two 

 caoutchouc tubes, and they are kept closed by the thumb and 

 forefinger of the left hand so as to be capable of instant and 

 simultaneous release ; the right hand is placed on the stopcock 



