The Necklace Storm Glass comes on a silver plated necklace. Pendant is 1.5" Fitzroys Stormglass historical weather and storm predicting device in the form of a necklace you can predict the weather on the move The storm glass was popularised by Admiral Robert Fitzroy after his historic voyage on the HMS Beagle. How the Storm Glass works is still a mystery, but it is believed that electromagnetic changes in weather patterns activate the crystals inside (sealed glass chamber fill with crystals when air pressure decreases). This is a gorgeous decorative gift idea for the adult who has everything or someone who finds meteorology fascinating.