1878.] Films under the Action of Sonorous Vibrations. 73 



which bright concentric rings contrasted with a differently tinted 

 ground, while the whole was snrronnded by a margin of mixed 

 colours in an unorganised condition. Stronger bowing, or the pro- 

 gressive thinning of the film, would then establish fig. 2, the most 

 typical and persistent of the whole series. Here concentric circular 

 bands were enclosed by others approximately square, and these again, 

 together with four sets of irregularly flattened ovals symmetrically 

 disposed, by other square bands, inclined at 45° to the former ones. 

 Outside the latter were four pairs of colour-vortices, with stationary 

 tadpole-shaped nuclei, rotating in the alternate directions shown by 

 the arrows. Nearly the whole space included between the outer square 

 and the edge of the film was occupied by colours whirling in circular 

 or slightly elliptic orbits. The contrast between the fixed and moving 

 portions of this figure was always extremely striking and beautiful. 



In fig. 3, a set of fixed concentric rings separated adjacent pairs of 

 vortices. 



Figs. 4 and 5 presented a pentagonal arrangement with five pairs 

 of vortices. The dotted space in the latter figure appeared speckled 

 over with minute air-bubbles. 



Fig. 6 belonged to a less regular class of forms. 



Fig. 7 was only once observed. Its central rings were inclosed in a 

 series of triangular bands, outside which were three sets of flattened 

 ovals similar to those in fig. 2, but each containing a single vortex 

 rotating about a nucleus. 



Fig. 6 usually showed itself only when the thinning of the film was 

 far advanced. There was a flow of colour along the dotted lines in 

 the direction of the arrow, which subsequently divided into two 

 streams, and, after passing outside the two sets of flattened ovals and 

 through the channels separating them from a third irregular crescent- 

 shaped series of bands, united again opposite the protuberance in the 

 concavity of the latter, and went on performing the same circuit. 

 When the film had become excessively thin, this figure frequently 

 showed nothing but the two tadpole nuclei, with an oval vortex about 

 each, whose longer diameter was not much less than that of the film 

 itself. 



In all the preceding figures the axis of symmetry was evidently 

 determined by the direction in which the sonorous vibrations reached 

 the film. 



The results which have been as yet described were obtained from 

 films clinging to the circular orifice of a resonator. A simpler mode of 

 proceeding is to form the film on an aperture cut in a piece of card- 

 board or thin sheet of metal, and place this upon the open end of a 

 resonance-box, into which its appropriate tuning-fork has been pre- 

 viously screwed. The box is, of course, to be held steady, with its 

 opening horizontal, while the fork is thrown into vibration. By 



