I. SOURCES. 179 



T~>vo metallic vibrators, each with a small speculum, are fixed at right 

 angles to each other, and sounds are produced by a current of air acting on 

 one or both of them at pleasure. The perpendicular vibrator is tuned to a 

 given note, and the horizontal vibrator is fitted with a mechanical arrangement, 

 whereby its pitch can be graduated to any degree of nicety within the compass 

 of two octaves. An apparatus is also provided with a means of concentrating 

 a pencil of light upon the speculum of the perpendicular vibrator, whence it 

 is reflected to the speculum of the horizontal vibrator. For educational pur- 

 poses, artificial light may be used, which can bo further reflected and magni- 

 fied upon a screen so as to be visible to a number of spectators. 



When musical sounds are produced by the vibrations, various luminous 

 geometrical figures are formed on the horizontal speculum, which, being thence 

 thrown on the screen give the curves described by the pencil of light, by the 

 single or joint action of the vibrators, and the form and motion of such figures 

 demonstrate the exact relation to each other of the musical notes produced. 



Sounds which harmonise to the ear, produce regular figures to the eye, as for 

 example, segments of the circle, ellipses, ovals, or straight lines, and if the 

 amplitude of each vibrator be equal, these luminous figures will appear on the 

 speculum or screen with an apparent steadiness. If the sounds do not 

 harmonise, the figures are confused, unsteady, and complicated. 



The mathematical relations of musical notes can also be demonstrated by 

 this instrument ; regular simple forms being produced by combinations of 

 those notes which result from vibrations bearing a definite numerical ratio 

 to each other, while irregular and unsteady figures are caused by notes which 

 have no such ratios. 



This apparatus has advantages over those in which tuning forks are used 

 for a like purpose; (L) In being able to prolong the effects to any period 

 desired by the operator ; and (2.) In its capability of representing combina- 

 tions and graduations otherwise unattainable. 



694. Photograph of a Chemical Harmonica of glass for 

 gas-flames, with eight pipes (major-scale from d l to d 2 inclusive), 

 with double regulating cocks, and key-board for playing. 

 With a copy of a few melodies executed on the same for two 

 and three voices. 



Prof. J. Joseph Oppel, Frank fort-on-the-Maine. 



The glass tubes can be turned by means of metal mountings, and can be 

 adjusted according to the height of the flames, which being regulated by the 

 taps, and the acoustic effect of the major and minor accords (particularly 

 when carefully tuned) are astonishing. 



695. Diapason Tuning Fork. F. Ernecke, Berlin. 



695a. Diapason of 200 double vibrations, arranged for 

 continuous action. T. Hawksley. 



695b. Model of a Scientific and Musical Instrument 

 called the Pyrophone, invented by the exhibitor, composed of 

 a series of glass tubes of different lengths and dimensions, in which 

 gas jets, when ignited and moved by a very simple apparatus, 

 produce the most perfect musical notes, and establish the new 

 scientific principle of the " interference ' : of melodious flames. 



Frederic Kastner, 43, Rue de Clichy, Paris. 



M 2 



