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Webster 1913 Edition

Adj.

Giving particular attention; habitually attentive to what passes; observant{1};

as, an

observing

person; an

observing

mind.

–

Ob-serv′ing-ly

adv.

ppr.

s as z.

Taking notice by the eye or the intellect.

Remarking.

Keeping; adhering to in practice; fulfilling.

a. Giving particular attention; habitually taking notice; attentive to what passes. He is an observing man.

observing

observing ‎(plural observings)

observation
- 2009, Gilbert Ryle, The Concept of Mind: 60th Anniversary Edition (page 194)
  Sensations then, are not perceivings, observings or findings; they are not detectings, scannings or inspectings; they are not apprehendings, cognisings, intuitings or knowings.