The target is going to be announced by the BBC on Thursday after a vote by viewers.
The 1714 prize was to find a way to determine longitude at sea and was won by the Yorkshire clockmaker John Harrison. No one knows what suggestions have been put forward for the 2014 prize, but here are some which might:
Quicker travel links (UK to Australia in an hour)
Making the Sahara arable.
Supplying all energy needs from renewable sources.
A cure-all for disease.
A way to make packaging bio-degradable.
A cure for avarice