62 THE ART OF PROJECTING. 



CHLADNl'S EXPERIMENT. 



A glass plate of any form, if fixed by a clamp, will 

 give out a musical sound when a violin bow is drawn 

 across its edge. If the surface of the glass be strewn 

 with sand, the latter will be arranged in some symmet- 

 rical form. The glass plate may be prepared as for 

 the magnetic phantom, and the sand fixed after its 

 acoustical arrangement, and afterwards projected as an 

 ordinary transparency. It is generally best to exhibit 

 this phenomenon during the process of arrangement, 

 and this will require the fixtures for vertical projection. 

 The glass to be sounded is to be made fast, and so 

 placed that as much as is possible of it is over the con- 

 denser of the vertical attachment ; then the sand sprin- 

 kled upon it, and the focus adjusted for the upper 

 surface. 



When the bow is drawn, the sand is seen to arrange 

 itself according as the plate gives out one sound or an- 

 other, which depends upon the part of the plate that 

 is bowed, and where it is damped, also upon its form. 

 It is well to have round, square, triangular, and hex- 

 agonal pieces, eight or ten inches in diameter. 



To show water-waves upon a Chladni plate, Professor 

 Morton has devised the following way : A plate of glass 

 about a foot square is so held by its middle that one 

 corner covers the condenser of the vertical lantern. To 

 this corner is cemented a thin ring of soft rubber, of 

 about five inches in diameter, and into this water is 

 poured to the depth of one-tenth of an inch. Project 

 the surface of the water and then draw the bow across 

 the edge of the glass, as in the other cases, so as to 

 produce a musical sound. The water within the rub- 

 ber ring is thrown into a system of large waves, which 



