PREFACE, 
XX1 
ance with the instruments employed, or much 
thought regarding the methods of applying 
them: and although his logical powers kept 
him in general to the employment of a term in 
one uniform sense when he clearly discerned it, 
yet, in cases where he happened unconsciously 
to change the meaning, or to be unaware of an 
ambiguity, his inaptness at analysis precluded 
all chance of his subsequently correcting any 
deviation, and the very strictness of his deduc- 
tions only led him further into error. Starting 
from a given proposition, he would reason from 
it with admirable closeness, but he seems never 
to have been sent back, by the strangeness of the 
results at which he arrived, to a reconsideration 
of the principle from which he set out, nor to 
have been roused to a suspicion of some lurk- 
ing ambiguity in his terms. Hence it might 
have been predicted, that he would commit 
oversights in his premises and assumptions, for