Apple Motion 4 - Manual (Page 613)

To modify the particles’ appearance using the Emitter HUD
1 In the Emitter HUD, drag the Scale slider to the left to reduce every particle’s size so that
the individual particles are more identifiable.
2 In the HUD, click anywhere along the outer edge of the emission control and drag to
define a narrow segment that limits the range of the angle at which particles are created
(the emission range).
Both points defining the emission range rotate around the center of the emission control
symmetrically, so your initial wedge points to the right. As you adjust the emission range,
the particles rearrange themselves in the Canvas, enabling you to see the resulting effect.
613 Chapter 11 Working with Particles