APPARATUS
The atomizer injects the spheres into the viewing chamber. The electric field is produced by the parallel metal plates in side the viewing chamber. The charge on the spheres is picked up in the injection system because of the friction in the system. The light is to illuminate the charges against a dark background. The dark background is a piece of black tape on the back of the transparent ring separating the two metal plates. The apparatus must be leveled to provide a better environment for making precise measurements.
The microscope flips the view upside down so what you are looking at is the top plate is on the bottom, and visa versa. The gravitational force appears to be acting in the positive direction.