ON EXPRESSING THOUGHTS. 147 



instances, after making the greatest efforts, we only succeed 

 in conveying to the minds of others the roughest, coarsest 

 representation of a mental image which to us is distinct, 

 clear, and perfect in all its details. And it is well known 

 how much more fatiguing is the operation of expressing 

 than that of thinking and drawing conclusions mentally. 

 The results of a few hours' thinking, obtained without any 

 perceptible exhaustion and without any conscious effort, 

 may require many days' hard labour to reduce to a form 

 intelligible to other minds, and in this operation the bodily 

 health may suffer, as well as the mental vigour be impaired. 

 It would therefore seem as if thinking and cogitation 

 belonged to the class of actions which I have distinguished 

 as vita/, and which* are performed without waste or change 

 in constitution of material substance, while the expression 

 of thoughts undoubtedly involves material changes of the 

 most active kind. We may roughly compare the first to 

 the acts of an engineer who directs and controls a machine, 

 and the last to the work performed by the machine itself. 

 The engineer or superintendent, it may be said, merely 

 exerts a directing and controlling influence which has 

 nothing whatever to do with the combustion of coals or 

 the falling of the weights, uncoiling of the spring, &c. He 

 contributes nothing that can be weighed or measured 

 towards the work performed by the machine. He can 

 exist without the machine, and the latter may act without 

 him, yet we all know how very much the result produced, 

 as regards both the quantity and the quality of work per- 

 formed, is due to his interference. 



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