16? 



used by me, has with a small plug of cotton-wool a tone of reson- 

 ance equivalent to /,, without a phig to e,. The funnel in front of 

 it was different in either experiment. When it was simply a flat 

 wooden platter, a peculiar resonance was not noticeable. 



The degree of sensitiveness is inversely proportional to the size 

 of the mirror. A mirror of 2 mm. in diameter and 60 (i thickness, 

 hung up by a Woliaston tibre of 2 fx have thus far proved to be 

 the smallest dimensions for easy handling. In the same proportion 

 the auditory canal should also be made narrower. Since we 

 generally experiment on continuous waves (only e^ yields a sta- 

 tionary wave), the distance at which the mirror is placed is of little 

 consequence, provided it be axial. The sensitiveness is about inversely 

 proportional to the distance from the aperture. It is remarkable that 

 acoustic attraction will often concur in the case of powerful sounds. 

 It should be precluded by all means. ') Electric attraction is obviated 

 by connecting the auditory canal with the point, from which the 

 mirror is suspended, by a small metallic chain. Should rather high 

 tensions occur in the neigbourhood, also a conductive connection to 

 the earth should be constituted. 



In physiological experiments the walls of the space in which the 

 mirror is suspended, are generally lined with gauze, which method 

 was also followed by Zeknov. To this there can be liardly any 

 objection, when experimenting with receiving funnels, the progres- 

 sive sound being in large part transmitted to the mirror along the 

 artificial canal. What is conducted from other quarters may be 

 disregarded altogether. 



The atferent tube is fitted to a copper plate. A more accurate 

 axial position must be eflfected by means of three adjusting screws 

 at the foot of the apparatus. The distance from the mirror to the 

 aperture of the tube is determined by a horizontal measuring 

 microscope mounted on a heavy vertical LEiTZ-stand. 



§ 2. Physical measurement. 



If instead of experimenting on the intensity of audible sounds 

 we wish to determine the objective intensity of a pure sound- 

 motion, auricle and auditory canal are of course disturbances. For 

 this purpose a conduit of a more physical nature is desirable. 

 The simplest is either a tube or a cone. A tube, if short, is liable 

 to become a resonator with a very sharp and narrow resonance. 



1) Attraction seemingly acoustic, but in reality involved by eddies, will occur 

 with any fine puncture in llie canal or in the membrane. 



12* 



