#87 - British Discovery First Day Cover Stamps. Issued on 19 September 1967 this set of stamps commemorates, "four aspects of British discovery which have changed the course of modern living".
4d - Designed by Clive Abbott depicts a radar screen to pay tribute to Sir Robert Watson-Watt and his discovery and development of radar.
1/- Also designed by Abbott, celebrates Sir Alexander Fleming's discovery of penicillin and shows spores of penicillin.
1/6d - Designed by Richard Negus and Philip Sharland this stamp illustrates 2 jet engines on a VC10 aircraft to commemorate the invention of the jet engine by Sir Frank Whittle.
1/9d - Also designed by Richard Negus and Philip Sharland the final stamp in this set celebrates the work of John Logie baird and an invention we all enjoy - the television!
I always find it odd when different people design stamps in the same set as they always appear disjointed when put together with no consistency of type sizes, fonts, size of the Queens head or even overall layout/style.
Here's the First Day Cover Envelope (designed by David Gentleman) showing portraits of the inventors...
There are many more First Day Covers and stamps in the reference box - check them out here