LETTER XL 



" Take an octagon building ; paint each side of a different colour. 

 Fix eight men fronting severally each side. Call them away, and 

 ask them the colour of the building ; and each will give a different 

 account. Now, where does the falsehood lie ? Do the same exter- 

 nal colours produce different impressions on different eyes ? Is the 

 evidence of the senses uncertain ? Are there no fixed principles 

 of sensation ? No : the mistake lies in a false inference. Each man, 

 instead of confining his statement simply to the part which he saw, 

 declares that the whole building, which he did not see, is of the 

 same colour with the part that faced him. His senses are correct; 

 his belief would be correct, if he would not fancy more than he 

 really perceived. Shift the parties, and try if, when placed before 

 the same side, they all agree in seeing black, or blue, or red, or yel- 

 low, where the colour really exists." — Sewell. 



January 25, 1855. 



My Dear Sons, 



1. Professor Sewell, in his " Christian MoraU^'' 

 says truly that " all our knowledge is in fact a 

 perception of relations." And, after remarking that 

 our ideas of the relations that subsist among the many 

 and very various objects of our knowledge, necessarily 

 and intuitively spring up in the mind on the very per- 

 ception of the relations, he observes that when those 



