suitable for KS4+. The apparatus consists of an electromagnet housed in a plastic moulded case supplied with a heavy steel sphere, an electromagnet unit with connections for an external timer and a platform unit containing a microswitch and terminals for the external timer. Action: The sphere is released by moving the switch on the electromagnet to the upward position. This action simultaneously starts the timer. As the sphere hits the cork mat on the platform unit it activates a microswitch to turn off the timer. It is recommended that this only be used in conjunction with the Eisco Laboratory Timer (code 0945), which has an in-built power supply for the electromagnet.