This figure shows three images. Image (a) is a photo of ‘The cavalry manual of horse management’ by Frederick L. Devereux, Jr. Image (b) is a photo of an airtraffic control centre. Image (c) is a cartoon. It shows a man stood in front of two doors – the first is labelled ‘Vice-pres in charge of smoke’ and the second is labelled ‘Vice-pres in charge of mirrors’.