(61) 



other end is fastened, transversely to the direction of vibration, to 

 the vibrating prong of an electrically (h-iven tuning fork. Now, when 

 the Corti's arches are sufficiently loaded (with sponges, or, for 

 demonstrations, with a hollowed little board on which a drawing 

 has been stuck), the tension of the string being at the same time 

 regulated by means of a micrometer screw, it is possible to cause 

 the system to resound to the tuning fork so that with small deflec- 

 tions of the fork the deflections of the pars pectinata become very 

 large. 



In the experiments for study proper, it deserves recommendation 

 to attach pins to the wooden Corti's arches, on which smaller and 

 larger sponges can be stuck in various positions. As long as the spon- 

 ges are dry the whole system jiartakes in the vibrations. But when 

 water is dropped on them, which is sucked in by the sponges and 

 makes them heavier, the damping system is brought to rest and a 

 node is formed at the base of the outer pillar. The string can be 

 prevented from sinking down too much, by attaching the fixed extre- 

 mity of the Corti's arch to a spring, which keeps it up. The free 

 extremity of the arch is placed loose on the string. Sometimes it is 

 a little difficult to obtain only vertical movements of the string, 

 but by moving the fixed point of support of the string forward or 

 backward, one always succeeds in this. 



We find then : 



1. broad deflections of the pars pectinata. 



2. immovability of the pars arcuata. 



3. immovability of the Corti's arches. 



4. immovability of the loading mass. 



This immoMibility is not absolute, of course ; on the contrary, the 

 floor, the table, everything in the room vibrates under the influence 

 of the tuning fork, but the movements are infinitely small compared 

 with the excursions of the pars pectinata and are so insignificant, 

 moreover, that a photograph of the parts, called immovable, shows 

 absolutely sharp definition. On the same photograph the pars pectinata 

 is seen in the extreme positions, which it reaches with broad amplitude. 



The conditions of the model have purposely been so chosen that 

 they correspond in general outlines to the conditions actually found 

 in Corti's organ. A complete imitation is impossible, but Avithin the 

 limits of technical practicability we have reached here, without any 

 preconceived opinion, what can be achieved with the ordinary means 

 of the laboratory. Now if we may see in the described model a 

 more or less ha[)py imitation of reality and to this assumption we 

 are especially entitled by the manner of loading, then it follows that 



5* 



