Assertion: sight's axis | /r/HasProperty | the line
Facets:
Source sentences:
text: The axis of a telescope is the line joining the optical center of the object glass to the center of the eye piece.
text: The axis of bubble tube or level tube is the line tangential to the longitudinal curve of bubble tube at its middle point.
text: The vertical axis is the line about which the telescope can be rotated in a horizontal plane.