Fairs contain a mixture of attractions which can be divided into the categories of adult, teenager and child; usually including thrill rides, children's rides, sideshows and sidestalls. Originally a fair would also have had a significant number of market stalls, but today this is rare and most sidestalls only offer food or games. The first fairground rides began to appear in the eighteenth century, these were small and made of wood and propelled by gangs of boys. In 1868, Frederick Savage, an agricultural engineer from King's Lynn, devised a method of driving rides by steam. His invention, a steam engine mounted in the centre of the ride, transformed the fairground industry.