12 



A. M. Mayer — Researches in Acoustics. 



surfaces of the disk D by two delicate helical springs fitting 

 over the tube at S and S', between the flanges of A and B and 

 the standards P and P'. The tubes T and T' were as close as 

 possible to the disk while it rotated. The flanges A and B 

 were of such diameter that no sound could issue between them 



and the surfaces of the 



rotating 



disk, because the flanges 



Fig. 9. 



entirely covered the hole in the disk while this hole traversed 

 the tubes T and T'. A tube of caoutchouc led from the tube 

 T' to the ear. 



Although a film of oil was between the flanges and the disk 

 and the disks were so accurately made that the greatest depar- 

 ture from uniformity of thickness amounted to only -J- S mm i J e ^ 

 the sounds produced by the sliding of the disk between the 

 flanges caused much distraction in the perception of the sound 

 from the resonator, which was adapted to the tube, T, of £ cm 

 in diameter. The results obtained with this apparatus agreed 

 with those given by apparatus (A). 



(D) I had formed great hopes of having the best apparatus 

 for the determination of the duration of a residual sensation 

 in the one shown in fig. 10. A is the lower drum of a Helm- 

 holtz double siren. D, the perforated disk of the siren, which 

 was rotated by the driving-wheel W. The disk, D, was 

 inclosed in the cover, C, of the form shown in fig. 10, clamped 

 to the drum of the siren. The sound issued from the box, 

 thus formed, and was conveyed to the ear by the tube E, to 

 which was attached a tube of caoutchouc. The sound to be 

 experimented on was conveyed from the fork, F, and resona- 

 tor, R, through a long tube T to the drum of the siren. By 

 placing pulleys, P, of various diameters on the axle of the 



