A. Nephoscope
B. Stethoscope
C. Metroscope
D. None of the above
Explanation:
A nephoscope was an instrument for measuring the altitude, direction, and velocity of clouds in the 19th century. A ray of light of known velocity is emitted from a nephoscope, which strikes the base of a targeted cloud. The travel time of the return signal is used to estimate the distance to the cloud.