Observations on Visible Vibration. 19 



112. It has been already stated, that we were at first dis- 

 posed to account for the transference of the powder from 

 the exterior to the interior surface of the glass by consider- 

 ing the lighter particles of the powder to be shaken from 

 the glass, carried upwards by the current, generated in the 

 surrounding air, and so falling into the glass formed the 

 trains on the nodes or quiescent portions, but in the latter 

 and successful trials I soon found that this could not be, 

 because the trains were formed in an instant, before even 

 the bow was taken from the glass, and, indeed, it is easy to 

 see how the trains are formed : as soon as the glass is 

 vibrated the powder by a sort of centrifugal force rushes 

 upwards over the edge, falls into the interior, where a par- 

 tial vacuum is formed by the vibratory action, arranges 

 itself first into a series of innumerable circles distinct from 

 each other round the whole interior surface ; they are then 

 shaken off the vibrating parts of the glass, and accumulate 

 in heaps or trains up the nodes, forming fan shaped figures 

 for the lowest note, and lines for the upper notes, and all 

 this is the result of a moment. 



113. The fans and lines can be produced alternating in 

 the same glass, provided the bow be so managed that during 

 the first ^aZf-stroke the low note be produced, and the 

 second half-stroke produce the high note. In such case a 

 very pleasing figure results, which may be represented on a 

 flat surface as in the following figure. 



Fiff. 8.* 



* This figure was copied from the glass hy my friend, D. C. Read, Esq., of 

 SaUshury, whose Etchings are so well known in this country and appreciated on 

 the continent. 



c2 



