200 KEACTION- WHEELS. 



contrivances have, however, usually a form which 

 differs from that shown in the figure, although the 

 principle is the same ; the principal difference consists 

 in this, that in the apparatus shown in the figure, the 

 water is conveyed to the horizontal cylinder from 

 above, while the larger machines are so arranged tha 

 the water enters the wheel from below, by means 

 a tube which is connected water-tight with the hori 

 zontal cylinder without impeding its motion. Smal 

 wheels of a similar kind are often used as ornamental 

 additions to fountains. 



A reaction- wheel can be easily made as follows : a metal ring, 

 across which a strip of sheet brass is soldered, with a hole 2 or 3 

 wide, drilled or punched through it exactly at the centre, is fixed 

 with sealing-wax round the wider end of a lamp- cylinder. The 

 other end of the cylinder is fitted with a long cork, through which 

 three holes are bored lengthwise one at the middle, to admit a 

 piece of stout steel wire filed to a blunt point at one end, and two 

 near opposite sides, to admit glass tubes. The piece of steel wire 

 should be 2o mm longer than the cork, so that it may be put quite 

 through the cork and still project 2 cm below the cylinder when the 

 cork is pushed 5 mm into the cylinder. It must be fixed very 

 firmly in the cork ; a hole is therefore made in the cork with the 

 bradawl, but is not widened, care being taken that it is bored quite 

 straight, so as not to give a slanting direction to the point. 

 A glass tube, 25 to 30 cm long and 4 mm wide, is drawn out in the 

 middle until the width of the thinnest portion is reduced to 

 l mm '5 ; a scratch is made at that point and the tube broken in two. 

 The points thus produced should not be fine and long, but rather 

 short ; to obtain such points, the tube must be continually turned in 

 the flame and drawn out at once ; if the tube is allowed to become 

 soft before it is drawn out, the points become too long and fine for 

 our purpose. Both tubes are twice bent at right angles, 2 or 3 cm 

 from each end, but so that the pointed end may be horizontal when 

 the other end is vertical. The holes for the tubes are bored through 

 the cork on opposite sides of the steel wire and at equal distances 

 from it. The whole being put together in the manner shown in fig. 

 144, the cork is fixed with sealing-wax, with the help of the blow- 



