rticularly the one shown in FIGURES 3, 4 and FIGURES 2A and 2B are a plan view and a side view respectively, illustrating a first embodiment of the apparatus of this invention; FIGURE 3 is a side view illustrating a second embodiment of the apparatus of this invention; FIGURE 4 is a cross sectional side view through the axis of the apparatus shown in FIGURE 3; and FIGURES 5A to 5D are views illust