16 Mr, Charles Tomlimons 



breathed upon, and tlie sex-nodal division produced by 

 the bow. In the process of vibration while the particles 

 of dust were becoming somewhat agglutinated by the con- 

 densing breath, the motion of the mercury underneath 

 arranged the film into a form analogous to that which the 

 mercury had itself assumed ; when vibration had ended 

 and the mercury become quiescent, the film retained the 

 figure which had been impressed upon it as in figure 6. 



Fig. 6. 



This figure assumes the appearance of having been caused 

 by a repulsion of particles from each vibrating centre, shew- 

 ing the inward bellying of the arc of the glass at each centre, 

 and exposing the surface of the mercury by its vibratory 

 action while at the nodes the powder is not disturbed. The 

 point at which the bow is applied becomes a centre of 

 vibration, and such, indeed, is always the case. 



105. The nodes having thus been indicated by means of 

 wires, mercury, water, and oil, endeavours were frequently 

 made to ascertain their existence by means of a dry glass 

 and lycopodium, as in the case of glass plates and other 

 plane surfaces, and for a considerable time our patience 

 has been tried unsuccessfully to accomplish on the surfaces 

 of goblets that which is affected by such simple and easy 

 means on plane surfaces. 



106. It was obvious that the only favourable form of 

 glass was the before mentioned conical vessel. Powder 

 was lightly sifted upon the interior surface, and the glass 

 then vibrated without the desired effect, the glass was 

 vibrated and the powder sifted into it during vibration, 

 but this was also unsuccessful, and after many such plans 

 the following was resorted to with success. 



