Sentence:  But then I had the [massive] flintlock by me for protection. ¶...The linen-press and a chest on the top of it formed, however, a very good gun-carriage; and, thus mounted, <WSD>aim</WSD> could be <WSD>taken</WSD> out of the window at the old mare feeding in the meadow below by the brook,nb.... 
Meaning of the word marked with <WSD> tags:  To position oneself and/or one's weapon so as to be aimed specifically at a chosen mark or target ("which is indicated after 'at''')