Prototypes built by researchers at the Naval Research Laboratory, Stanford University and Philips, a Dutch electrical-goods firm, can detect a substance that is present at a concentration of less than one part in a million billion.

ECONOMIST: Labs on a chip

Don Melrose, also at Sydney, points out that the gas in the middle of the galaxy might already be so strongly ionised, and thus such a good electrical conductor, that current would leak away rather than build up into a concentration like the Snake.

ECONOMIST: Here be serpents