[pravda]

The schematic is wrong, the relay and diode should be moved to be 'on top' of the transistor. But the circuit on the perfboard looks correct.

The diode goes across the relay coil because when the relay coil is turned off, there will be an inductive spike generated. The diode protects the transistor.

[dps]

Thanks for pointing this out, folks - I made a mistake in the original circuit diagram. It's now fixed.