226 



OPTICAL PROJECTION 



rubber blowing-tubes to be cut off. The two bubbles being 

 projected and outer taps closed, on now opening the tap which 

 places them in communication, the small bubble will expel its 

 contents into the larger one. 



The effect of surface tension on masses of fluid may be 

 projected in various ways. A small circular vessel being 

 focussed on the screen, it can easily be shown that it may be 

 filled with liquid far above the level of the rim. In the 

 cubical tank, the spherical shape taken by a mass of olive or 

 castor oil, in a mixture of alcohol and water of the same 

 specific gravity, may be projected as in fig. 115, direct. Even 

 Plateau's experiments on the modified forms produced by 



rotation of the mass, may be 

 partially projected in the same 

 simple manner ; but to show 

 the actual detachment of a 

 ring of oil at a given velocity, 

 the vertical method must be 

 employed. The manner will 

 suggest itself, but fig. 116 

 shows the apparatus as ar- 

 Flo 115 ranged by Stohrer. The rays 



from the condensers fall at 



45 upon the reflecting mirror s,, to be directed upwards. In 

 the field is placed the cubical tank G, with a glass bottom p, 

 held by the screw m l . By the screw m 3 is adjusted the 

 revolving arrangement, consisting of a perpendicular rotating 

 wire provided as usual with a small tin disc near the bottom 

 to carry the sphere of oil, and a small pulley w at the top, by 

 which this is rotated from the larger pulley w. By the screw 

 m 3 the whole can be adjusted for height and in the centre of 

 the field; and in Stohrer's apparatus revolution is effected 

 by a .thread e fastened to the endless cord which embraces 

 both pulleys, but I myself should prefer a winch-handle. 

 Highe-r up the pillar v, which is attached to the mirror-box 



