INDUCTION IN CURVED LINES — IN FLUIDS, SOLIDS. 19 



towards them that the lateral tension or mutual repulsion of the lines of force before 

 spoken of, (1224.) by which their inflexion is caused, is so much relieved in other 

 directions, that no inductive charge will be given to the carrier ball in the posi- 

 tions A-, /, m, n, o, p, (fig. 7-)' A very good mode of making the experiment is to let 

 large currents of the gases ascend or descend through the air, and carry on the ex- 

 periments in these currents. 



1227. These experiments were then varied by the substitution of a liquid dielectric, 

 namely, oil of turpentine, in place of air and gases. A dish of thin glass well covered 

 with a film of shell-lac, (1272.) and found by trial to insulate well, had some highly 

 rectified oil of turpentine put into it to the depth of half an inch, and being then placed 

 upon the top of the brass hemisphere, (fig. 7-) observations were made with the carrier 

 ball as before (1224.). The results were the same, and the circumstance of some of 

 the positions being within the fluid and some without, made no sensible difference. 



1228. Lastly, I used a few solid dielectrics for the same purpose, and with the same 

 results. These were shell-lac, sulphur, fused and cast borate of lead, flint glass well 

 covered with a film of lac, and spermaceti. The following was the form of experiment 

 with sulphur, and all were of the same kind. A square plate of the substance, two 

 inches in extent and 06 of an inch in thickness, was cast with a small hole or de- 

 pression in the middle of one surface to receive the carrier ball. This was placed 

 upon the surface of the metal hemisphere (fig. 9.) arranged on the excited lac as 

 in former cases, and observations were made at n, 0, /?, and q. Great care was re- 

 quired in these experiments to free the sulphur or other solid substance from any 

 charge it might previously have received. This was done by breathing and wiping 

 (1203.), and the substance being found free from all electrical excitement, was then 

 used in the experiment; after which it was removed and again examined, to ascertain 

 that it had received no charge, but had acted really as a dielectric. With all these 

 precautions the results were the same ; and it is thus very satisfactory to obtain the 

 curved inductive action through solid bodies, as any possible effect from the transla- 

 tion of charged particles in fluids or gases, which some persons might imagine to be 

 the case, is here entirely negatived. 



1229. In these experiments with solid dielectrics, the degree of charge assumed by 

 the carrier ball at the situations n, 0, p (fig. 9.), was decidedly greater than that 

 given to the ball at the same places when air only intervened between it and the metal 

 hemisphere. This effect is consistent with what will hereafter be found to be the re- 

 spective relations of these bodies, as to their power of facilitating induction through 

 them (1269. 1273. 1277.)- 



1230. I might quote mani/ other forms of experiment, some old and some new, in 

 which induction in curved or contorted lines takes place, but think it unnecessary 

 after the preceding results ; I shall therefore mention but two. If a conductor A, 

 (fig. 8.) be electrified, and an uninsulated metallic ball B, or even a plate, provided 

 the edges be not too thin, be held before it, a small electrometer at c or at d, uninsu- 



D 2 



