Sentence:  Of this ridge Soutra hill is supposed to be the highest; but hitherto no actual <WSD>mensuration</WSD> is known to have been taken of it : but, in judging by the view, from its elevated top, of the neighbouring hills and country, it must be upwards of 1500 feet high. 
Meaning of the word marked with <WSD> tags:  The act or process of measuring; measurement.