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industry. And what is this experience of theirs ? A few years ago 

 it possessed exactly the same attributes as that which they now 

 designate theory, and it was gained, for the most part, from the 

 practice of those whom they designate theorists. This may be 

 shown by an example. The colouring properties of madder root 

 have been long known, and when it was first proposed to apply 

 this knowledge to the art of dyeing, there would doubtless be 

 considerable uncertainty whether the scheme would turn out to be 

 profitable. However, madder has been for many years extensively 

 cultivated in many countries of Europe and Asia, and England has 

 imported it to the value of a million of money annually. The 

 transition from theory to practice is here well exemplified. About 

 ten years ago, some one analysed the madder root, and found that 

 the colouring principle was a substance which was produced by 

 a kind of fermentation in the root, and which received the name of 

 alizarine. Two German chemists analysed the alizarine, and found 

 in it a substance called anthracene ; this they recognised, and 

 knew that it could be got from coal tar. Thus it was discovered 

 that alizarine could be got from coal tar. That the colouring 

 principle of the madder root can be manufactured from coal tar is 

 merely an item of knowledge ; but the knowledge, coupled with 

 the proposal to use coal tar as a substitute for madder, is regarded 

 as theory. There is no question as to whether the dye from one 

 source is as effective as that from the other ; the question is whether 

 it would be profitable and expedient in every way to give up the 

 cultivation of madder and use the artificial instead of the vegetable 

 dye. This question remains to be answered. 



Theory and experience are, therefore, not two distinct 

 species, but the same in different stages of development. Thus 

 far it seems that theory and practice are mutually implicated in all 

 our industrial achievements. In estimating their relative value in 

 the progress of nations, we are apt to confine our attention too 

 exclusively to such men as Watt, Stephenson, Cooke, VVheatstone, 

 Cyrus Field, or Holmes, who applied knowledge to useful purposes, 

 and to leave out of the question those who created the knowledge 

 so applied — men who have spent long years of hard labour in the 



