The Science Museum now holds a collection of over 300,000 items , including such famous items as Stephenson 's Rocket , Puffing Billy ( the oldest surviving steam locomotive ) , the first jet engine , a reconstruction of Francis Crick and James Watson 's model of DNA , some of the earliest remaining steam engines , a working example of Charles Babbage 's Difference engine ( and the latter , preserved half brain ) , the first prototype of the 10,000-year Clock of the Long Now , and documentation of the first typewriter .
The Science Museum holds over 300,000 items , including such famous items as Stephenson 's Rocket , Puffing Billy ( the oldest surviving steam locomotive ) , the first jet engine , a remake of Francis Crick and James Watson 's model of DNA , some of the earliest remaining steam engines , a working example of Charles Babbage 's Difference engine ( and the latter , preserved half brain ) , the first prototype ( draft model ) of the 10,000-year Clock of the Long Now , and documentation of the first typewriter .