Digital Companion to C. S. Peirce
1895 [c.] | On the Logic of Quantity | MS [R] 17:8

Observation is properly voluntary self-preparation to be promptly affected by that experience which we have learned will be irresistable at last; but the word observation comes to be applied to the sensory elements in the whole process of being affected by cognitive experience …

1898 | Training in Reasoning | RLT 182-3

Observation consists of two parts which though theoretically they have much in common yet practically are of almost contrary natures. The first is a sort of subconscious induction, by which upon repeatedly reviewing an object of perception a certain element of it acquires great associational potency, – that is, has a magnified tendency to call up other ideas. [—] The other part of observation consists in moulding in the upper consciousness a more or less skeletonized idea until it is felt to respond to [the] object of observation. [—]

Observation may also be divided into three nearly independent genera according to the different natures of the elements observed. Namely, it may be directed to the qualities of objects or to experiential facts of relation, or to relations between the parts of an image one’s own phantasy has created.