the world > physical sensation > sight and vision > optical instruments > instruments for observing > [noun] (59)
(a) a tube through which observations are made; (b) a transparent tube connected to a tank or cistern so as to display the level of the liquid…
Subcategories:
— receptacle for objects (1)
— light or radiation (10)
— stereoscope (11)
— comparator (4)
— for viewing photographs (4)
— thaumatrope (4)
— stauroscope (2)
— stroboscope or oscilloscope (5)
— for observing other phenomena (6)
— scanning devices (6)
— for surveillance (1)
— eyephones (1)
— parts of (1)
— observation with (1)