538 Dr. William E. Stone [March 18, 



The following diagrammatic table was exhibited : — 

 I. Mechanical Methods. 



1. Savart's toothed wheel. 



2. Cagniard de Latour's siren. 



3. Perronet Thompson's monochord. 



4. Duhamel's vibroscope. 



5. Leon Scott's phonautograph. 



6. Edison's phonograph. 



II. Optical Methods. 



1. Lissajous' figures. 



2. Helmholtz's vibration-microscope. 



3. Koenig's manoraetric flames. 



4. McLeod and Clarke's cycloscope. 



III. Photographic Methods. 



1. Professor Blake's experiments. 



IV. Electrical Methods. 



1. Meyers' electrical tonometer. 



2. Lord Rayleigh's pendulum. 



V. CoMPUTATiVE Methods. 



1. Chladni's rod tonometer. 



2. Scheibler's tuning-forks. 



3. Appunu's tonometer with free reeds. 



4. Koenig's tuning-fork clock. 



Under the first heading, an exact copy of Colonel Perronet 

 Thompson's monochord, and the siren ; under the second, Lissajous' 

 figures, and McLeod's ingenious modification of these in the cycloscope 

 were demonstrated, the latter having proved one of the most accurate 

 and satisfactory instruments hitherto employed for this purpose. 

 Considerable stress was laid on the fifth or computative method, on 

 account of its extreme simplicity and accuracy, and also on the fact 

 that by it. Absolute had first been obtained from Relative pitch. 



The three instruments mainly adverted to were Scheibler's 

 Tonmesser, Appunn's reed tonometer, and Koenig's tuning-fork 

 clock. The first and second of these were exhibited ; of the third 

 a photograph was projected on the screen. Scheibler was a silk 

 manufacturer, of Crefeld, in Germany, who as early as 1834 pub- 

 lished his system of pitch-measurement. In its simplest form, it 

 consists of sixty-five tuning-forks, each beating with its two neigh- 

 bours four times per second, the first and last producing together a 

 true octave free from beats. It can easily be shown mathematically 

 that if the product of 64 X 4 which = 256, and is the sum total of 

 beats, be correct, it must equal the vibration-number of the deeper 

 and half that of 512 the acuter fork. Thus absolute will have been 

 deduced from relative vibrations, and the problem of pitch-determina- 

 tion will have been solved. Scheibler's excellent observations, 

 however, seem to have failed to meet with the recognition they 

 deserved, until they were disinterred by Helmholtz and his English 

 translator, Mr. Alex. J. Ellis. 



