811 



photographic registering apparatus, which he very kindh' placed at 

 our disposition, and for whicii we gladly express our sincere thanks 

 to him once more here. 



Anorij. Cht'm. Luboniton/ of the Universit//. 



Amsterdam, Oct. 28, 1915. 



Physiology. — '-On iifdir-soumk." By Dr. ¥. Roei.s. (Oornmuni- 

 cated l)y Prof. Dr. H. Zvvaardkmaker). 



(Communicated in the meeting of October 30, 1915). 



In daily life after-sounds are rarely perceptible to the car of 

 normal man and even then lliey are vagne and comparatively feeble 

 after violent detonations. We, therefore, had to apply rather potent 

 stimuli and to screen our subjects from all disturbances above all 

 from the ordinary street-noises. 



The Galton- and EoKi.MANN-wliistles gave most satisfaction. The 

 subject was placed in the camera sileuta of the Physiological Lal)0- 

 ratory at Uti'echt : the head was fixed, ihe right ear at 2 cm. dis- 

 tance and right in front of the embouchure of the whistle. At every 

 time an airstream of equal force was urged through the whistle by 

 the experimenter outside the camera. In the first experiments the 

 whistle was put into operation inside the camera by the experi- 

 menter, who also recorded (he phenomena perceived l»y the subject. 

 Although we used our utmost endeavour to do this as noiselessly 

 as possible, it was detrimental to the production as well as to the 

 observation of the phenomena. We, therefore, resolved to separate 

 the experimenter from the subject. They spoke to each other bv 

 telephone, which enabled the experimenter to perform Ihe time- 

 measurements liy means of a chronometer. The subject used the 

 telephone only for these measurements ; for the description of the 

 nature of tiie phenomena he relied entirely upon his memory after 

 the experiment. This procedure was not open to objection as the 

 phenomena never took more time than I'/, minute. 



Before entering upon our experiment proper a series of respectively 

 100 and 50 preliminary tests were performed with our two subjects. 

 Prof. Dr. A. Michottk from Lou vain and Dr. Bakkkr from Batavia. 

 The total number of the subsequent conclusive tests amounted for 

 M to 143 and for B to 129. 



