818 SEC. 18. BIOLOQY. 



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 vision, 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 coloured by a red glass either way. Thus either 

 two sounds, two lights, or a light and a sound, can be made perceptible 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. 



3996. Noematograph. Registering the time of physical 

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

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



The instrument consists of a horizontal cylinder, which, on being turned by 

 the hand, moves in a spiral. The cylinder is covered with smoked paper, 

 upon which a tuning fork with 250 vibrations per second, to be struck by a 

 percussion hammer, registers its vibrations by means of a small steel spring. 

 This tuning fork can slide and rotate on an axis by which it is suspended. 



Without any further complication, the cylinder with tuning fork is sufficient 

 for experiments with the simplified phonautograph, whose spring registers its 

 vibrations next to those of the tuning fork. Two persons A. and B. sit before 

 the phonautograph. A. shouts a short vocal sound, B. repeats it as quickly 

 as possible ; on the line registered by the spring the instants of the shouting of 

 the sound by A. and B. are visible, and the time can be read on the adjoining 

 chronoscopic curve. The experiments to be made are : a. B. knows which 

 vocal A. will produce ; b. B. does not know which vocal (from two, three, or 

 more) A. will produce ; c. B., not knowing which vocal he is going to hear, 

 has to respond only upon a certain one, e.g., on a. The L time for the inter- 

 vening psychical processes may be deduced from the times ascertained in the 

 experiments , 6, and c. 



For other experiments the instrument is more complicated. At one end of the 

 cylinder are two rings partly covered with copper, partly with ebonite. On 

 each ring two pair of electrodes rest ; the lower break and close a constant 

 current, the upper an induction current. The electrodes together are attached 

 by a thick glass bar to a horizontal board following the cylinder, moving in a 

 spiral, thus keeping the electrodes on the rings. The induction currents pass 

 the tuning fork. In a series of experiments only the inner ring is used (the 

 outer ring can be moved aside). On this ring quadrants of copper and ebonite 

 alternate. The electrodes rest on copper, the tuning fork is struck, the cy- 

 linder moved half a turn ; at the instant the lower electrodes leave the copper, 

 the induction current makes a hole in the paper on the chronoscopic curve, and 

 a spark is made visible without being audible, or audible without being visible, 

 or, the spark being neither audible nor visible, a shock is felt. The spark passes 



