From the MEWS photo archive, this Crampton locomotive was displayed at an Alexandra Palace event by the North London Model Engineering Society. 

In the 1840s, when Thomas Crampton, who was a versatile engineer, was developing his designs for the steam locomotive, it was thought that a low centre of gravity (hence a low-slung boiler) and large, rear-mounted driving wheels (for speed and stability) were necessary for success. At first, he designed some unusual-looking engines, but these evolved into what we now regard as the classic Crampton – four or six small carrying wheels beneath the boiler, and two driving wheels mounted behind the firebox. 

There was relatively little weight on the driving wheels; to improve adhesion, it was found necessary to put cast iron weights beneath the cab footplate. These engines were not very popular in Britain, where there were only 42 in use, mainly in the Kent area, but there were large numbers in regular use on the continent, especially in France and Germany, and smaller numbers in Denmark, New Zealand, North America and other countries.