306 FLOW THROUGH TUBES OF UNEQUAL BORE. 



3 or 4 mm thick, with a piece of brass wire passed through a hole 

 it, and bent at right angles, renders the wrapping on of 

 cord more easy ; the handle is placed in the hollow at the top of n\ 

 and replaced by the wheel as soon as the cord is wrapped round th 

 spindle. The cord should of course be wrapped round the spindl 

 in such a manner that, on unwinding it, the wheel is turned upward 

 into the air ; in the figure the wheel is a left-handed screw an 

 (looking down upon it from above) it must be turned from left t 

 right, as the hands of a watch move, in order to make it rii- 

 upwards ; the cord must therefore be wrapped on from right to lef 

 and if the small handle be used it must be turned in a direction of 

 posite to the motion of the hands of a watch. The last turn of tb 

 cord should be close to the disc o* metal, so that it may be presse 

 between the latter and the preceding turn, and the cord be thus pr< 

 vented from unwinding itself. 



When everything has been tLus prepared, the part g is held in tl 

 left hand, the arm is stretched out horizontally and the cord firm 

 pulled off by the right hand ; the wheel will rise in the open a 

 about 10 m , and return to the ground again after 6 or 8 seconds. " 

 a room it rises to the ceiling, rebounds and returns to the floor whe 

 it continues to spin round like a top. 



Remarkable phenomena may be observed whe 

 liquids and gases flow through tubes which becon 

 suddenly wider at one point, or when gases escape fro 

 orifices into the open space. If water flows in vaci 

 through a tube, which becomes wider at a short distan- 

 from the end, the jet will either pass freely through tl 

 widened part, without filling it, as shown in fig. 202 - 

 or, if considerable adhesion should exist between t 

 tube and the liquid, the latter would flow along t ; 

 side wal] of the tube in the wider part of it, as repr 



sented at B. If the orifice be closed for a short tini 



. 



the wider portion of the tube becomes completely fille i 

 but when the orifice is opened again the efflux proceed 

 as before, as soon as the quantity of water collected i 

 the wider part has been discharged. The reason of tl ; 

 is easily understood. If a liquid passes through a tu - 



