The author's excellent 'powers of observation' [=ability to notice and pay close attention to things] are evident in the book's detailed descriptions.
The plants seem to have recovered from the disease, but they are still 'under observation'. [=someone is watching them carefully]
They're keeping him at the hospital 'for observation' [=so that doctors can watch him carefully] for another few days.
(..) Randy... Stevie Wonder wears one, or do you rank on him, too? Honey, please. It's all right, Gloria. I enjoy Randy's observations. My wife's name is Gail, Frank. Can you hear that? Gail. Excuse me. Gail. Gail strikes me as a very beautiful woman, but, you know, (..)1992 Scent of a Woman