Are fernlike crystals building up? A storm is on the way. Star crystals drifting downward? Expect frost. Clear liquid? Clear and dry. A trusted weather predictor for 250 years (Admiral Fitzroy used one "on the Beagle during his voyage with Darwin in 1750), the Weems will alert you to what?s coming a day or two in advance. Brass cylinder with sealed glass chamber stands upright, secures to a fl at surface, or mounts on the engraved display plaque (sold separately). 1 ü" diameter, 6 ý" high; plaque is 10" x 8". From Weems & Plath, makers of fi ne nautical instruments for more than 80 years.