On Sonorous Vibrations. 253 



tiiey fall, but fly about ; this hinders them from pursuing a 

 regular progressive movement, like that of sonorous undula- 

 tions. It was on this account that, on varying my exper;-» 

 nients, I thousjht of substituting in the place of sand, a more 

 attenuated matter not possessing the inconveniences I have 

 mentioned ; this was semen lycopod'u, or the seeds of club- 

 mess. After having covered a plate of metal or glass with 

 this substance, I tried to produce a sound in the manner of 

 Chladni, and in an instant I saw the dust distribute itself in- 

 to a number of little regular tumuli, which put themselves 

 in motion at their extremities, or formed the figures discover- 

 ed by this naturalist. They always range themselves in the 

 form of a curve, the convexity of which is in proportion to 

 the point touched by the violin bow, or towards the point 

 \yhich has an analogous situation : the nearer that each of 

 these little heaps is to these points, its height is the more 

 considerable ; this gives to the whole a remarkable regularity. 

 The experiments of JNI. Chladni are astonishing at first 

 sight, on account of the regularity of the figures produced 

 by a single stroke of the bow, which appears as if done by 

 magic. My experiments have not the same charm ; but 

 perhaps they are more instructive, on account of the com- 

 parative slowness of my process, which admits of their effects 

 being more advantageously studied,. We observe that the 

 interior of the small elevations formed in my experiments 

 continue in motion during the continuance of the sound. 

 The duration of these vibrations, although very short, is ap- 

 preciable on plates of three or four inches diameter : it is 

 longer when plates of a larger diameter are employed. I 

 often made use of a disc of metal of six inches diameter : iu 

 this case I always saw tlie small elevations change their ap- 

 pearance at different epochs of the duration of the sound. 

 At one moment the height increases, and at another it di- 

 minishes, and the dust has the appearance of arranging 

 itself in small globules which roll one above another: we 

 easily perceive that all these phtenomena are still very com- 

 plicated. The movement of the grains is in part vertical, in 

 jiart horizontal ; the horizontal movement is composed of 

 two others; cue of the forces impels the grains forward, and 

 1 the 



