HELMHOLTZ IN KONIGSBERG 



ing my lectures, I was led to devise the method of 

 measuring the velocity of the nervous impulse, and 

 also to the conception of the ophthalmoscope. This 

 instrument became the most popular of my scientific 

 achievements ; but I have already pointed to the 

 oculists how much good fortune, rather than any 

 personal merit, favoured me in its invention. - I was 

 endeavouring to explain to my pupils the emission of 

 reflected light from the eye, a discovery made by 

 Briicke, who would have invented the ophthalmo- 

 scope had he only asked himself how an optical 

 image is formed by the light returning from the 

 eye. In his research it was not necessary to ask 

 it, but had he asked it, he was just the man to 

 answer it as quickly as I did, and to invent the 

 instrument. I turned the problem over and over to 

 ascertain the simplest way in which I could demon- 

 strate the phenomenon to my students. It was also 

 a reminiscence of my days of medical study, that 

 ophthalmologists had great trouble in dealing with 

 certain cases of eye disease, then known as black 

 cataract. The first model was constructed of paste- 

 board, eye lenses, and cover glasses used in the micro- 

 scopic work. It was at first so difficult to use, that 

 I doubt if I should have persevered, unless I had felt 

 that it must succeed ; but in eight days I had the 

 great joy of being the first who saw before him a 

 living human retina.' 



It had long been known that the eyes of certain 

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