166 PHILOSOPHY OF ZOOLOGY. 
pression its common or peculiar character. Our knowledge 
“of objects, therefore, in reference to any particular sense, will 
be in proportion to the number of impressions, continued a 
sufficient length of time, which have been made upon that 
sense. In early life, we cannot analyse an impression, with 
any degree of accuracy, because we have few former ones 
with which to compare it. As we advance in life, our im- 
pressions increase in number, and consequently, our capabi- 
lity of analysing any one of them. In youth, we know but 
few of the relations of an impression ; and, after a rapid and 
superficial examination, we turn away to a new object. In 
more advanced life, we can trace, in any impression, a much 
greater variety of relations to other impressions, and in do- 
ing this, we occupy much longer time in its examination. 
To this circumstance, we are disposed to refer the fickleness 
of children. When a new object is presented to them, they 
are much gratified ; but as they can speedily trace its more 
obvious relations to all their former superficial impressions, 
it speedily loses its interest. If these observations be cor- 
rect, we never could acquire an accurate knowledge of a 
solitary impression produced on any one of the senses; all 
our accuracy, on this subject, being the result of comparison. 
When the senses are thus employed, in investigating the 
nature of impressions,—the objects which produce them, 
and the circumstances by which they are modified, they 
then become, what the leaders in the science of Mind have 
been pleased to denominate—orGaNs OF PERCEPTIONS. 
The knowledge we acquire of the relations of an impres- 
sion, 1s usually termed idea, sometimes perception. The 
last phrase, however, is frequently used indiscriminately, to 
denote the presence of the impression,—the attempt to ana- 
lyse its charaeter,—or the knowledge which results from the 
examination, We are disposed to use Sensation to express 
