The act or the faculty of observing or taking notice;
the act of seeing, or of fixing the mind upon, anything.

The result of an act, or of acts, of observing; view;
reflection; conclusion; judgment.

Hence: An expression of an opinion or judgment upon
what one has observed; a remark.

Performance of what is prescribed; adherence in
practice; observance.

The act of recognizing and noting some fact or
occurrence in nature, as an aurora, a corona, or the structure of an
animal.

Specifically, the act of measuring, with suitable
instruments, some magnitude, as the time of an occultation, with a
clock; the right ascension of a star, with a transit instrument and
clock; the sun’s altitude, or the distance of the moon from a star,
with a sextant; the temperature, with a thermometer, etc.