( 424 ) 



a way tliat the sound may be listened to tliroiigli a caoutchouc tube 

 in the cabinet. This organ-pipe is permanently blown by air which 

 w^as supplied by a presspump driven by water and afterwards dried 

 with chloride of calcium. The supply of this air takes place along 

 a long system of leaden tubes, which shows inside the cabinet a 

 division into two parts and afterwards a reunion. To this two sepa- 

 rate branches by micrometer screws removable diaphragm openings 

 of AuBERT are attached, which may be widened oi' nai-rowed at 

 pleasure. The i-eunion takes place in a T-tap, which may also be 

 directed by the investigator, and down the current are placed the 

 necessary measuring apparatus for determinijig the pressure and 

 volume of the air passing to the organ-pipe. These measuring appa- 

 ratus are placed within the reach of the investigator, so that he 

 himself can do the reading off. 



The investigator arranges in the first place the width of the two 

 diaphragm-openings in such a way that the sound may be called 

 equal in the two positions of the tap. Then he enlarges one of the 

 diaphragmata (the other remains constant) till a distinct difference is 

 perceived (ascending method). This he does live times. After this the 

 difference between the two tone intensities, which were alternately 

 listened to, was enlarged and the diai)hragm jjosition was ascertained 

 by descending at which the difierence became indistinct (descending 

 method). This again was done live times. The same takes place con- 

 formally in narrowing the diaphragm-openings. So the first series 

 leads to a "obere" the second to an "untere Unterschiedsschwelle". 

 The determinations which were made for each tone with two chief 

 intensities have evidently taken place "wissentlich" in this way. At 

 last a pressure and volume determination of the supplied air is made 

 for the found diaphragm widths. The fii'St takes place by means of 

 a watermanometer, which for increasing sensibility has been put 

 sloping; the second with an aerodromometer^). The energy offered to 

 the organ-pipe could be calculated with the usual formula e ■=. air- 

 volume X pressure X ^8i. Tlii^ number, multiplied by a constant 

 factor, different for each pipe, indicates the acoustic energy. 



As in the expression of the "prozentische Unterschiedsschwelle" 



AD 



the constant factor occurs both in the numerator and the deno- 



R 



minator, the constant factor of the organ-pipe falls away from 



the further calculation and we can also come to a trustworthy result 



of the "prozentische Unterschiedsschwelle" without its preceding 



1) Arch. f. (Anat. u.) Physiologie 1902 supplement, p. 417. 



