493 



voorn (hit'klj padded witli horseliair) : a, 3 (5), ais, 5, h^ 1 (3), c, 1 

 (5), ds, 2 (3), <1, 1 (2), d!s.^ 1, e, J, f, 1, fis, 1, ^, 3 (2), yis, 2\/, 

 (1), </, 4 (2), ais, 3 (2), />, 2, C3 2, cw, 1, d, 1, dis, 1 (2), C3 4 (6) ^). 

 The procedure is quite simple. At a distance of 'J m. the organ 

 pipe is sounded twice, tone for tone, once with the hearing apparatus, 

 another time witli the comparison-funnel. The reinforcement is ex- 

 pressed in the ratios of both numbers. 



§ 2. Hearing-apparatus loith selection, lüithout the aid of foreign 

 energy. 



In the publication alluded to above, an endeavour was made to 

 classify hearing apparatus as follows: 1. contrivances substituting a 

 deficient conducting apparatus, 2. apparatus bringing the sound 

 generator nearer" to the listener, 3. apparatus aflbrding an enlarged 

 receiving capacity, 4. apparatus reinforcing a certain group of tones, 

 5. apparatus reinforcing ihi'ough foreign energy. 



P'or shortness sake only the last two groups are discussed in the 

 present paper. 



Most of the ear-trumpets used by deaf people belong to the 

 apparatus mentioned sub 4. In them the reinforcement is occasioned 

 not only by selection, but also by the widening of the receiving 

 surface and by shortening the distance from the speaker. This is a 

 peculiar feature of Guyf/s apparatus, which is largely used in our 

 country. Tested by Lord Rayleigh's mode of arrangement it yields 

 the following results, illustrating the reinforcement of every single 

 tone : (see table 494). 



The most reliable of these determinations is the One in the first 

 column. With the old method the resulrs were liable to be misleading 

 in virtue of undue selection of certain tones. With our method this 

 is out of the question, there being no other resonance than that 

 which is always present in the human ear itself (meatus, auricle). 



The specimen of Güye's apparatus that we examined this time, 

 reinforces the discant of the speechzone; the one investigated in 1912, 

 acted similarly upon the bass as we found by electric measurement. 

 An improved specimen of modern type (copper spiral along the 

 border of the inner receiver, the inside of the latter being covered 

 with velvet) also intensifies the discant more than the bass. It 

 appears that the new models are discant-intensifiers and that their 

 influence is distributed evenly over a wide range. To make assurance 

 double sure, 1 subjoin the results of a measurement in the camera 

 silenta, i.e. free from all room-resonance. 



') The figures in brackets apply for determinations made in anollier room. 



32* 



