Mysterious stuff in a glass tube

As it's shaping up to be my final days in Devon, me and my #1 Nerd travelled to Barometer World, a pilgrimage we'd been promising to make since the start of summer. As the name suggests, it's a Mecca of meteorological wonder, boasting hundreds of aneroid and mercury barometers, barographs, thermometers, hygrometers and thunder bottles. It's a bargain at £2.50 and I encourage everyone to go. What intrigued me most of all, though, was the strange crystals attached to many of the old barometers. This, I was told, was storm glass, a curiosity whose origins are hidden in the mists of time. Back in…