A!N AUTOBIOGRAPHICAL SKETCH. 273 



I plunged then with great zeal and pleasure into 

 the study of all the books on physics I found in 

 my father's library. They were very old-fashioned ; 

 phlogiston still held sway, and galvanism had not 

 grown beyond the voltaic pile. A young friend and 

 myself tried, with our small means, all sorts of experi- 

 ments about which we had read. The action of acids 

 on our mothers' stores of linen we investigated 

 thoroughly ; we had otherwise but little success. 

 Most successful was, perhaps, the construction of 

 optical instruments by means of spectacle glasses, 

 which were to be had in Potsdam, and a small 

 botanical lens belonging to my father. The limitation 

 of our means had at that time the value that I was 

 compelled always to vary in all possible ways my plans 

 for experiments, until I got them in a form in which I 

 could carry them out. I must confess that many a 

 time when the class was reading Cicero or Virgil, 

 both of which I found very tedious, I was calculating 

 under the desk the path of rays in a telescope, and I 

 discovered, even at that time, some optical theorems, 

 not ordinarily met with in text-books, but which I 

 afterwards found useful in the construction of the 

 ophthalmoscope. 



Thus it happened that I entered upon that special 

 line of study to which I have subsequently adhered, and 



which, in the conditions I have mentioned, grew into 

 IL T 



