It was believed that tropical animals could not survive outside in London's cold weather and so they were all kept indoors until 1902, when Dr Peter Chalmers Mitchell was appointed secretary of the Society. He set about a major reorganisation of the buildings and enclosures of the zoo, bringing many of the animals out into the open, where many thrived. This was an idea inspired by Hamburg Zoo, and led to newer designs to many of the buildings. Mitchell also envisaged a new park to the north of London, and in 1926 Hall Farm, near to Whipsnade village, was bought. In 1931, Whipsnade Wild Animal Park opened, becoming the world's first open zoological park. The first woman to be a curator at the London Zoo was Evelyn Cheesman, in 1920.