Here's how the word works in the sentence:
* Hebetudinous: This word describes a state of being dull, sluggish, and slow.
* Atmosphere: This refers to the overall feeling or mood of the library.
* Palpable: This emphasizes that the feeling of hebetude is so strong that it can be felt physically.
This sentence paints a picture of a place where even the air itself seems to have lost its energy and vitality.