The Collaborative International Dictionary of English v.0.48:

Weatherglass \Weath"er*glass`\, n.
   An instrument to indicate the state of the atmosphere,
   especially changes of atmospheric pressure, and hence changes
   of weather, as a barometer or baroscope.
   [1913 Webster]

   Poor man's weatherglass. (Bot.) See under Poor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

weatherglass
    n 1: a simple barometer for indicating changes in atmospheric
         pressure