Two curious inventions: Roper's steam-powered motorcycle (1869- bottom) and Daimler's gasoline motorcycle (1885- top).

An interesting, personal review of Douglas Hoftadter's book, fittingly titled "Gödel Escher Bach: An Endless Geek Bible". This book is one of the only three "Further Reading" suggestions I gave at the end of my popular science book on quantum computing.

There is actually a clock called QuantumGravity.