2i8 HERMANN VON HELMHOLTZ 



I feel myself too much of a dilettante, to others, and remain on 

 the firm ground of natural science to which I am accustomed/ 



This splendid work, which was intended for the instruction 

 of an extensive public in the literary world, was widely read, 

 but could be understood as a whole only by a chosen few, 

 since not a little training in physics and even mathematics 

 was indispensable for its real appreciation. On February 27, 

 1864, Helmholtz writes to Ludwig, in answer to his expressions 

 of amazement at the stupendous production : 



' I am delighted that you are satisfied with my Sensations of 

 Tone, because you are one of the few musical men of science 

 who I can hope will succeed in understanding the whole. The 

 book appears to me so far to have had rather a succes d'estime, 

 than any real effect in convincing people. Not that I had ever 

 cherished any illusions to the contrary. At all events I see 

 that it has made an impression, and venture to hope that it will 

 gradually win its footing.' 



While his Sensations of Tone was passing through the press, 

 Helmholtz had occupied himself almost exclusively with prob- 

 lems in physiological optics, and was now engaged, in connexion 

 with his work on the horopter, upon a series of ingenious ex- 

 periments, and a profound mathematical analysis of the very 

 difficult subject of the movements of the eye, and their relation 

 to binocular vision, in which he referred all the theorems 

 previously discovered by himself and others to one single law, 

 that of the simplest orientation in space. He published these 

 researches at length in Graefe's Archiv f. Ophthalmologie, with 

 the title, 'On the Normal Movements of the Human Eye/ 

 After it had been proved by Bonders' experiments that the 

 purpose of single binocular vision is not promoted by the move- 

 ments of the eye, Helmholtz endeavoured to find an optical 

 law for eye-movements, starting from the conviction that an 

 organ so well adapted to its functions as the eye, must fulfil 

 some optical aim in these movements also. He arrived at this 

 law by a further development of that of simplest orientation. He 

 connected the proposition that every given position of the line 

 of vision corresponds with a given degree of rotation of the 

 eyeball, with the question how the latter is retained during its 

 movements, or how it has .become possible for the eye to 

 remain accurate in its orientation when the fixation point in the 



