nephelodometer

from The Collaborative International Dictionary of English v.0.48

Nephelodometer \Neph`e*lo*dom"e*ter\
   (n[e^]f`[-e]*l[-o]*d[o^]m"[-e]*t[~e]r), n. [Gr. nefe`lh a
   cloud + "odo`s way + -meter.] (Meteorol.)
   An instrument for reckoning the distances or velocities of
   clouds.
   [1913 Webster]