444 



in welcher die kurzen Linien, von denen die Radien durchkrcuzt 

 m werden, die Axen der Theilchen anzeigen, wel- 



j che die Radien bilden. Oder was dasselbe ist 



wenn n der Mittelpunct der Oeffnung ist, so 

 K&. miissen die Linien nm, n o, n p, n q u. s. vv. 



\ 



\ \\Uz 



0. 



\ dieselbe Structur haben, wie Prismen, deren 



/ depolarisirende Axen mit der Lange und Breite 



der Prismen zusammenf'allen. 



Die scheinbare Griisse der Biischel ist etwa = 4°, dieselbe wie 



die des Foramen, und des von mir entdeckten schwarzen Fleckes 



von abweicbender Empfindlichkeit. 



Dass eine radiale Structur vorhanden ist, wird (lurch ver- 

 schiedene Versuche bewiesen, durch die schnelle Bewegung der 

 magischen Scheibe (auch durch Galvanismus) , wiihrend welcher 

 gelbe und blaue Lichtbiischel, so wie andere merkwiirdige op- 

 tische Erscheinungen zum Vorschein kommen '). 



M ,,I have found it very difficult to examine a phenomenon in which the 

 light is so feeble. I think however it is certain that the yellow tint is 

 one of the 1st order, and my notion was that it is produced by the po- 

 larising structure of the cornea, and the crystalline lens and its cap» 

 sule , the analysis being effected by the different spherical transparent 

 membranes which lye between the Lens and the real Retina, acting like 

 ■ a number of thin watch glasses. 



This structure however though it would explain the existence of 

 four luminous sectors, two yellow and two blue does not explain what 

 I regard as the peculiar and remarkable part of the phenomenon, namely 

 the fact that the two yellow sectors or bushels lye in the plane of 

 primitive polarisation and not in the plane of 45°. 



Hence as there is no known structure in the Bye when its parts are 

 examined by polarised light, (which are capable of producing luminous 

 sectors lying in the plane of primitive polarisation, we must look for 

 the structure necessary to produce your phenomenon, in the Retina and 

 the different membranes of which it is composed. 



Adopting this idea the foramen centrale, or the central portion of 

 the Retina, if it is not a hole, must be surrounded with the structure 

 necessary to produce luminous sectors which lye in the plane of primi- 

 tive polarisation , and in the plane perpendicular to it, the yellow in the 

 former, and the blue in the latter, as the complementary colour of the yellow, 



The required structure must therefore be circular, or one consisting 

 of radial lines directed to the same centre, the particles composing .-the 

 radial lines, having (heir axes inclined 15° to those lines, 



