i 5 o HERMANN VON HELMHOLTZ 



wanting, and different persons form a different judgement, 

 some seeing a mixed colour, others irregular specks of colour. 

 From this Helmholtz deduces the all-important conclusion that 

 the sensation from each eye'comes separately to consciousness, 

 so that simple vision with both eyes is not the consequence 

 of an anatomical junction of the nerve-fibres, but the result 

 of an act of judgement. 



In September, 1854, Helmholtz writes from Konigsberg to 

 A. Fick : 



' I have been busy for some time over my Physiological Optics. 

 I cannot make it all as popular as the doctors would like, but 

 I have tried to arrange so that what they do not care for is 

 put together, leaving the rest for them. I have not covered 

 much of the ground yet, because I began with the hardest 

 parts, refraction, accommodation, &c., and was tempted into 

 making new and systematic measurements on the living eye, 

 which have only resulted in the conclusion that the human 

 eye is so irregular that exact measurements do not repay one. 

 I have also made a number of experiments on colour There 

 are so many vexed questions in physiological optics that can 

 be settled by a couple of accurate experiments, that one is 

 ashamed to bandy words about them, without making the 

 experiments, so that I really see no prospect of getting on 

 any faster.' 



Part I of the Handbook appeared in 1856. Meantime, with a 

 view of establishing the subjectivity of sensation for the other 

 senses also, and of determining the psychical processes by which 

 we understand these sensations, Helmholtz had been turning 

 his attention to physiological acoustics, in which he again 

 opened up an entirely new field of physiological discovery, 

 and in which his results were as admirable as those he obtained 

 in physiological optics. 



On May 21 he writes to Wittich : 



' During the winter I reinvestigated the connexions of the 

 auditory ossicles, and worked at Tartini's tones. I am so far 

 ready that I have sent a resume to the Academy at Berlin, 

 and am now working at the longer paper. I hope to derive 

 the whole theory of harmony from the fundamental fact that 

 the ear perceives movements that are regularly repeated at 

 given intervals as a continuous sensation of tone, and that 



