968 SEC. 18. BIOLOGY. 



stripes have one direction, and then turned round a horizontal axis passing 

 through these stripes until the two perpendiculars 011 the first stripes are also 

 parallel. (By this contrivance we find the position for close work with the 

 hands, which, according to Bonders, has in course of time determined the 

 angle between meridians of apparent equal direction.) 



3993. Spark-Stereoscope, with coloured lenses, showing 

 stereoscopic vision independent of movement of the eye. Archiv 

 fur Ophthalmologie, Band xiii. p. 33. Prof- Bonders, Utrecht. 



A box with two apertures for the eyes. A series of very small induction- 

 sparks is used as object of fixation. Between two electrodes attached to the 

 sliding lid of the box, we may cause a large spark to pass at different dis- 

 tances before and behind the object of fixation. In monocular vision we fail 

 in recognising the place of the large spark with regard to the object of fixa- 

 tion ; but in binocular vision, at the first spark we judge correctly. Between 

 the apertures for the eyes are other electrodes. The spark passing between 

 these last two electrodes is out of sight, but its two reflex images are seen 

 on a coloured lens ; one image is coloured the other not. In binocular vision, 

 their position with regard to the object of fixation is soon distinguished ; but 

 without an object of fixation, many sparks are required for accurate estima- 

 tion. In general such coloured lenses are very convenient for demonstration 

 and mutual comparison of the reflex images of concave and convex surfaces. 



3994:. Ftoto stereoscope, to determine the relative value of 

 the second eye for binocular vision, constructed upon the principle 

 of Her ing. Prof. Danders, Utrecht-, 



The balls made to fall from the curved rod appear at the respective dis- 

 tances under equal angles, and seem to pass with equal velocity through the 

 field of vision, so that every indication for the monocular vision is excluded, 

 and the relative value of the second eye, for stereoscopic A r ision, can be 

 deduced from the relation between the number of correct and incorrect cases 

 (according to Fechner's method). 



3995. Noematachometer. (Onderz. physiol. laboratorium, 

 Ser. 2, II., bl. 92, 1868). Prof. Donders, Utrecht. 



A vertical board with a central slit for the eyes, above a sliding electro- 

 magnet with a long metallic prism suspended. The prism has in front and 

 behind a pair of sliding arms upon which a rod can rest, and at its back part 

 two small sliding metal wire-frames, which can contain a very small piece of 

 burning coal. On closing the current the prism falls, and is received in a 

 box with asbestos underneath the slit. During the fall, the rods meet re- 

 spectively a wooden and a metallic arm, and each produces its characteristic 

 sound ; the frames with incandescent coal pass the slit one to the left, the 

 other to the right, and one or other at pleasure coloured by a red glass. Thus 

 either two sounds, two lights, or a light and a sound, can be made percep- 

 tible with changeable difference of time (by sliding prism, rods, and frames), 

 and in this manner we learn the time between two impressions, with increasing 

 changes (correct and incorrect cases, Fechner) to perfect certainty, which 

 enables us to judge about the priority of two impressions. 



/. PSYCHICAL PHENOMENA. 



3996. Noematachograph. Registering the time of psychical 

 processes. (Onderzoekingen physiol. laborat. Ser. 2, D., 1st. 21.) 

 Archiv fur Anat., u, s. w. 1868. Prof. Bonders, Utrecht. 



