5G A CHEMICAL TRIAD. 



The affection of colour blindness has been noticed by Dai- 

 ton's biographer, Dr. Angus Smith, as perhaps supplying a 

 key to some of that great philosopher's traits or peculiarities, 

 especially the dogged persistence wherewith he advocated views 

 based on evidence unperceived or incomplete to other people. 



Dalton's character was deficient in idealism. He was an 

 indefatigable hunter after facts truths. Adopting these as 

 a basis, he arrived at deductions which had been heretofore 

 mere poetic dreams begotten of ardent fancies ; thus affording 

 another example of the frequently noticed fact, that the fic- 

 tions of poets and ideal speculations, however wild they seem, 

 are often the shadows of truth unseen as yet, but slowly ad- 

 vancing towards the goal of discovery. An engraver on cop- 

 per, affected with colour blindness still more completely than 

 Dalton only being able to distinguish in the varying tints of 

 colour, gradations of white and black testified that he con- 

 sidered the affection an advantage. He was not subject to 

 the difficulty of being able to decide on the amount of white- 

 ness or blackness of which each tint of colour should be ren- 

 dered in the engraving. May not the colour blindness of 

 Dalton have imparted increased tranquillity and power of 

 concentration of other faculties ? May not the field of his 

 intellectual excursions have been rendered more free from 

 obstacles, in proportion as his sense of vision was narrowed ? 

 Might not the sum of intelligence remaining to him have 

 been increased by the extent of the amount taken away ? c It 

 would probably explain many strange occurrences,' writes 

 Dalton's biographer, 6 if we were to consider that there are 

 really persons in the world who see all crimsons as " dark 

 blue" or "a muddy blue," and who would match crimsons 

 with claret or mud, pinks with light blues, browns with reds, 

 and drabs with greens ; who see the healthful tints of a florid 

 complexion to be like "dilute black ink on white paper," or 

 "a dull opaque blackish blue upon a white ground." How 

 many strange mistakes and visions might be accounted for by 



