PROFESSOR AT HEIDELBERG 247 



relation to the conduction of auditory oscillations, Helmholtz dis- 

 cusses the vibrations of the petrosal bone and endolymph, on 

 the basis of Kirchhoff s theory of the conditions of equilibrium 

 in an infinitely slender elastic rod, investigates the considera- 

 tion of the anatomy of the tympanum, and proceeds farther to 

 the form of a membrane stretched by air-pressure alone, with 

 inextensible radial fibres. 



The completion of this work, which is a model of the most 

 delicate dissection, of the most ingenious physical methods, and 

 of the profoundest mathematical analysis, took up the whole of 

 the winter after Helmholtz had communicated its elementary 

 details at Heidelberg in the summer of 1867. In August, 1867, 

 he went to the Ophthalmological Congress held in Paris during 

 the Great Exhibition, and gave a lecture ' Sur la Production de 

 la Sensation du Relief dans FActe de la Vision Binoculaire\ in 

 which he outlined some of the new work published in his 

 Physiological Optics. 



' Yesterday and the day before/ he writes to his wife on 

 August 14, 1867, ' I spent the mornings at the Ophthalmological 

 Congress, where they made a great deal of me. Graefe is here, 

 but unfortunately neither Bonders nor Bowman. I was solemnly 

 received with acclamations by the Society, and then had to 

 promise a lecture, which I delivered early yesterday morning in 

 French, of course ex tempore as there was no time for pre- 

 paration. ... I was invited to the Society's Banquet at Vefour's ; 

 the first toast was proposed by Graefe in my honour, to which I 

 had to reply, and later they toasted me again in a poem made by 

 Bowman's friend Critchett, and seconded by a young Spaniard, 

 in this style : " L ophthalmologie etait dans les tenebres, Dieuparla, 

 que Helmholtz naquit Et la lumiere est faite ! " You will see I 

 had to forget how to blush ! ' 



All the letters written from Paris to his wife, who was on the 

 Tegern See with the children, betray his regrets that she could 

 not be with him, since her long residence there in former 

 days would have led her to enjoy the stir of the Exhibition, 

 and intercourse with all the distinguished persons staying there 

 at the time, even more than he did himself. 



1 Still,' replies the wife, ' since God has cut our poor Robert 

 off for ever from a normal existence, he must and will be our 



Irst charge. It was perhaps my greatest sorrow to forgo this 



