SOURCES OF SCIENTIFIC IDEAS. 51 



ference from immediate ones, and are sometimes called 

 conceptions. Many ideas are a mixture of immediate 

 conscious perception and inference. 



All our primitive sensations and emotions communicate 

 to us immediate ideas ; what we feel, we do feel without 

 usually requiring to compare, generalise, or employ our 

 reason, and without being largely able to prevent it. But 

 in receiving immediate ideas, we require to obey the rules- 

 of correct observation ; and, to perceive them correctly,, 

 our senses must be educated. Even then we are apt to 

 make mistakes ; and we probably never perceive with, 

 perfect accuracy. 



Mediate ideas are inferences; for example, perception 

 of 'distance : we do not see it, but infer it. As from a 

 single fact many inferences may be drawn, so mediate 

 ideas are far more numerous than immediate ones, and 

 include not only all general ideas, laws, principles, causes, 

 and coincidences, but all those made known to us by the 

 testimony of other persons ; all our beliefs of past and 

 future events, and of those events which occur in our 

 absence, and of which therefore we have no immediate 

 consciousness, except such as is revived by the memory. 



All scientific ideas and terms may also be divided into 

 qualitative, or those which do not include the notion of 

 magnitude, and quantitative ones, or those which include 

 that idea ; for instance, the simple conception of existence 

 of a thing is a qualitative one, but that of the extent 

 to which that thing exists is quantitative in addition. 

 Although each qualitative idea does not, in its abstract 

 form, include the notion of magnitude, yet, in many 

 cases, when compared with other ideas, a vague impres- 

 sion of relative magnitude arises. The first glimmering 

 of an idea of a thing is that of its simple existence ; but 

 that is a very faint conception, although the most funda- 



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