Determine e in two ways. You can let a selected sphere fall through a measured distance with no electric field present, then apply an electric field and observe the velocity of the rising sphere. Or, you can allow a sphere to fall freely, then apply a high-voltage field until the sphere is suspended. The spheres do not need a radioactive source to charge.

Built in to this top-quality, compact tabletop unit are all the accessories you need to perform Millikan experiments -a microscope, an illuminator, a 0-500 VDC voltmeter, latex sphere solution, and all the necessary power inputs. Simply carry it to a lab table, plug it into a 110 VAC outlet, and it's ready to use. For added convenience, the spray bottle system features a reservoir that attaches to the side of the unit so you don't have to look away during the experiment.

Controls include:

• An on-off switch
• A polarity-reversing switch
• A potentiometer for fine control of plate voltages
• A voltmeter for indicating plate voltage