In the second world war Mr Pierce worked on radar, in which signals directed at an object are bounced back to the transmitter.

ECONOMIST: John Pierce

This broad metaphor also lent itself to sub-metaphors, including object-icons such as a rubbish bin (also the work of Mr Mercer when he worked at Apple in the 1980s), folders and files.

ECONOMIST: Metaphorically speaking

If such an object were detected, astronomers would have three days to confirm their calculations, under procedures currently being worked out by the International Astronomical Union.

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