HELMHOLTZ IN HEIDELBERG 



forearm that is, moving it so as to direct the palm 

 upwards, he is of opinion that the real supinator is 

 the biceps, and that the so-called supinator longus 

 is a real flexor. The strongest supination, when the 

 arm is stretched, is brought about by the simultane- 

 ous action of both biceps and triceps, and when the 

 arm is flexed, then supination is brought about by 

 the biceps alone. The action of the palmaris longus 

 comes into play when the hand is made hollow, and 

 it appears to protect the flexor tendons from the 

 pressure of the folded skin. Finally, he showed that 

 in the flexed position, the first phalanges can be 

 rotated round their own axis by the interossei 

 muscles, a movement which had not previously been 

 observed. 



The movements of the eyeballs were of great 

 interest to Helmholtz, and he solved some of the 

 difficult problems of single vision with two eyes. He 

 had, as he himself remarked, a gift of seeing things 

 in their geometrical relations, so that he was able to 

 deal with questions of this nature with the greatest 

 ease. In the year 1862, there appeared the first 

 paper on the form of the horopter, that imaginary 

 field in space, rays from any objects on which must 

 fall on corresponding points of the two retinae, and 

 consequently give rise to the sensation of a single 

 image. The year 1863 saw two papers on the move- 

 ments of the human eyes, giving an account of 

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