In the early years of the 19th century William Smith and his pupil John Farey began to apply stratigraphic principles to the sinking of water wells. Between 1840 and 1870 engineers, such as Robert Stephenson, and geologists, such as James Clutterbuck, Joseph Prestwich and David Ansted began to make systematic observations. After 1870 Geological Survey officers, particularly William Whitaker, Joseph Lucas and Charles de Rance, became involved in groundwater work. Lucas introduced the term hydrogeology and produced the first British hydrogeological maps. The first half of the 20th century was a period of missed opportunities with the significant advances in hydrogeology taking place in mainland Europe and North America. The Water Act of 1945 marked the start of a new era in which the Geological Survey and, after 1965, the Water Resources Board led the way. Hydrogeology is now a mainstream branch of geology in Britain and interest in the subject is such that the Hydrogeological Group of the Geological Society has a membership of around 1050.