The entire city was an ice rink. A half-foot of new snow, followed by a freak warm spell with meltwater running on the sidewalks - then a refreeze - had swirled in to create the worst conditions ...

The surface of ice is a slippery subject. For more than 160 years, scientists have been debating the quirks of ice’s exterior. Frozen water is coated in a layer of molecules that behave like a liquid.