42 Mr. J. W. Swan. Stress and other Effects 



phase of the phenomena described. Figs. 1 and 2 represent in profile 

 the appearance at the middle and final stage of the action. 



Fig. 1. — Positive. Nearly Maximum Effect. 



FlG. 2. — Positive. Maximum Effect. 



If a metal ring (of 90 mm. diameter) is substituted for the disc, similar 

 but more sharply defined effects are obtained. When the arrangement 

 described is varied by making the ball oyer the basin negative, instead 

 of positive, on breaking the primary circuit there is less displacement 

 of the viscid material consequent on repeated interruptions of the 

 circuit. To obtain a characteristic effect of repeated negative dis- 

 charges, the spark-gap should be widened to 50 mm., and to prevent 

 sparking over the edge of the basin, it should be at least 150 mm. 

 diameter. There is then formed, immediately under the ball, a 

 concavity the counterpart in size and curvature of the ball, and 

 outside this there is the general figure, somewhat faint and tremulous, 

 which seems to be a complication of the positive and negative figures, 

 the characteristic positive figure encircling the more distinctly nega- 

 tive portion. Fig. 3 is a profile view of the negative displacement. 

 The extent of the effects described is considerably modified by the 

 degree of viscosity of the liquid, and this can be controlled by tem- 

 perature. 



Corresponding but modified phenomena are produced by means of 

 the Wimshurst induction machine. When, for example, an 8 mm. 

 metal ball connected to the + arm of the discharger hangs 15 mm. from 

 the surface of the resin and oil mixture of the consistency of treacle 

 contained in a large basin, and the — arm of the discharger is con- 

 nected to a metal disc of 100 mm. diameter under the basin, the dis- 

 charger balls being 75 mm. apart, the result of continuously working 

 the machine is the production of a turbulent motion, attended by the 



Fig. 3. — Negative. Maximum Effect. 



