produced in Resin, $-c, by Electrification, 43 



formation of vortices into which the upper stratum of the liquid 

 pours downward, carrying adherent air with it, while an equal and 

 opposite movement takes place from below, producing worm-like 

 eruptions of spirally twisting or wriggling jets of: liquid at the sur- 

 face. If the margin of the dish beyond the surface of the liquid is 

 thinly smeared with the viscid liquid, the film breaks up into dew-like 

 beads. 



With a metal ball of 150 mm. diameter, 6 mm. above the surface of 

 the liquid and a proportionately larger disc basin and depth of liquid, 

 acted upon by a machine of moderate power, the spark-gap being 

 adjusted so as to prevent sparks passing from the ball to the liquid, 

 and the tension such as to keep up a strength of electrification of the 

 surface only slightly less than that which would cause disruptive dis- 

 charges to pass, a column of liquid rises and connects the overhanging 

 ball and the surface of the liquid in a manner strongly suggestive of 

 water-spout phenomena. The ascent of the column of liquid is 

 followed by the descent of numerous thin surrounding streams, 

 and these keep up a regular system of upward and downward 

 circulation. 



Fixation of Characteristic Effects. — In order to fix the various forms 

 produced in the viscous mixture of oil and resin, an experiment was 

 made with nearly pure resin, rendered plastic by heat, and cooled to 

 solidity while under the action of electric discharges. It was found to 

 be difficult to carry this out in a satisfactory manner, but it suggested 

 a reversal of the procedure, viz., the electrification of a surface of 

 resin in a solid state, and the subsequent development of the stress 

 effect by rendering the surface superficially plastic by heat. This 

 mode of operation resulted in the production of permanent relief and 

 intaglio figures, corresponding to Lichtenberg's dust figures, to 

 Brown's photographs,* and to the dust figures and photographs more 

 recently described by Lord Armstrong. f 



The preparation of the resin surface for the production of the 

 permanent figures requires care. The method I employed is as 

 follows : — A thin glass basin was filled with a mixture of resin and 

 5 per cent, resin oil, the oil being added to lessen the tendency of the 

 resin to fracture on sudden change of temperature. The resin, 

 melted in a metal pan, was poured through a filter of muslin into the 

 basin, while embedded in small shot and raised to the fusion 

 temperature of resin. On slowly cooling, the basin being meanwhile 

 covered with a plate of glass or an inverted basin, the resin solidifies 

 with a smooth bright surface. The resin-filled basin was partly 

 covered, on the bottom, by a disc of tinfoil, and was placed centrally 



* ' Phil. Mag.,' toI. 26, p. 502. 



f ' Electric Movements in Air and Water, with Theoretical Inferences,' by Lord 

 Armstrong, C.B., F.E.S. London : Smith, Elder and Co., 1897. 



