494 Proceedings of the 



plate was made to revolve, the holes in the box were, therefore, opened 

 and closed sixty times in each revolution ; and when air was blown 

 through the box, musical sounds were produced, having a deter- 

 minate pitch, dependent upon the rapidity of the plate, or rather 

 upon the number of impulses given to the air by opening and shut- 

 ting the exit passages a given number of times in a second. 



A striking point in the character of this instrument is, that whe- 

 ther air or water be passed through it, still the pitch of sound is 

 the same for the same velocity of the plate, being not at all altered 

 by the density or rarity of the substance upon which the impulses 

 are given. 



A small musical instrument, recently invented in Germany, was 

 then produced, in which the sounds were caused by successive 

 impulses upon air, like as in the stop-cock of Professor Robison, 

 or the Syren of Cagniard de la Tour, except that, though simpler 

 in practice, the method was more complicated in principle. It was 

 called the Mund Armonica, and consisted of a plate of metal having 

 small rectangular apertures, about half an inch in length, cut in it 

 side by side : there were eight of these holes, and each was fur- 

 nished with a thin elastic plate of metal, which being fastened at 

 one end of the hole, was so adjusted in size as to vibrate freely 

 in the aperture, which it nearly filled. When the mouth was 

 placed over one or more of these apertures, and air urged forward, 

 it caused the spring to vibrate as it passed it ; these vibrations 

 produced so many impulses upon the current of air, and thus 

 caused sound. The plates are adjusted by their thickness, rigi- 

 dity, and other circumstances, to produce a certain number of vi- 

 brations in a given time, and so determine the pitch of sound. 

 The notes produced were very beautiful and clear, having much of 

 the character of those of the ^Eolian harp. 



It was stated that the Eol-harmonica, a keyed instrument, brought 

 from Germany into this country by Mr. Schulz, was constructed 

 upon this principle. Mr. Schulz and his sons, who were present, 

 illustrated the powers and effect of this instrument by various per- 

 formances. 



The principle of the Mund Armonica is distinctly described in 

 Professor Robison's works, p. 538, &c. where he suggests that it 

 will probably be found highly useful in the improvement of musical 

 instruments. 



May I6th. 



This evening Mr. Knowles concluded his account of the rise, 

 pto^ress, and present state of Naval Architecture in Britam. 



