APPENDIX. 445 



the velocity and the volume of the discharge. The funnel-shaped 

 tube prevents the formation of cross currents by leading the liquid 

 more gradually to the point of exit. 



APPENDIX F. 



Barker's Mill. A working model of this apparatus ( 264) 

 may be easily made by any wide-awake pupil. Select a long, sound 

 lamp-chimney and a fine-grained cork that snugly fits the lower end. 

 Take a piece of glass tubing, the size of a lead pencil, heat it intensely 

 in an alcohol or gas flame until you melt off a piece a little shorter 

 than the lamp chimney. By reheating the end thus closed by 

 fusion, you may give it a neat, rounded finish. Prepare four pieces 

 of glass tubing, each 12 cm, long. These pieces would better be 

 made of tubing smaller than that just used. To cut the tube to the 

 desired length, scratch the glass at the proper point with a tri- 

 angular file, hold the tube in both hands, one hand on each side of 

 the mark just made, knuckles uppermost and thumb-nails touching 

 each other at a point on the tube directly opposite the file-scratch, 

 push with the thumbs and at the same time pull with the fingers. 

 The tube will break squarely off. Smooth the sharp edges by soft- 

 ening in the alcohol flame. Bend each of these four pieces at right 

 angles, 2 cm. from each end, in such a way that one of the short 

 arms may be in a horizontal plane while the other short arm of the 

 same piece is in a vertical plane. The tubes may be easily bent 

 when heated red-hot at the proper points in the alcohol or gas flame. 

 See that the four pieces are bent alike. In the middle of the cork, 

 cut a neat hole a little smaller than the tube first prepared. Near 

 the edge of the cork, at equal distances, cut four holes a little 

 smaller than the four pieces of bent tubing. Push the open end of 

 the straight tube through the middle hole. From the other side of 

 the cork, enter one end of each bent tube into one of the four holes. 

 Place the cork with its five tubes into the end of the chimney, see- 

 ing to it that the straight tube lies along the axis of the chimney, 

 i. e., is parallel with the sides of the chimney. The closed end of 

 the central tube should be near the open end of the lamp chimney. 

 In pushing the tubes into the cork, grasp the tube (previously dip- 

 ped in soap and water) near the cork, and screw it in with a slow, 

 rotary onward motion. See that the bent tubes are at right-angles to 

 each other, like those shown in Fig. 91. For a support, take a piece 

 of stout wire, small enough to turn easily in the central tube, and a 

 little longer than the chimney. Place one end in the middle of a tin 

 pepper-box and fill the box with melted lead. This makes a firm 



