Giles Dilnot, so enthusiastic about his subject that at times the radio seemed practically to vibrate, began his account (15 January) of the Natural History Museum’s attempts to preserve its collections during wartime in the establishment’s main hall alongside “Dippy” the Diplodocus. At 26 metres long and the height of a ­double-decker bus, Dippy was by no means an easy object to evacuate – the preferred option for significant specimens – and down in the basement lay a treasure trove of less weighty companion pieces extending to nearly 80 million items.What was to be done? Made circumspect by their memories of the First World War, the museum authorities began their contingency plans as far back as 1933, when Hitler’s rise to power gave notice