Sentence:  At the same time another child - this one of Shelley 's brain - was given to the world : Alastor , a poem of pervading beauty in which the reader may gaze into the still depths of a fine <WSD>mind</WSD> 's musings . 
Meaning of the word marked with <WSD> tags:  that which is responsible for one's thoughts and feelings; the seat of the faculty of reason