DOVE ON THE ELECTRICITY OF INDUCTION. 175 



fore also be weakened by the addition of solid iron, and the 

 increased action with one spiral must pass through a stadium of 

 inactivity into a diminishing action when the number of spirals 

 is gradually increased. 



By a remarkable coincidence the conditions for inactivity were 

 exactly supplied by the two spirals, which, when it is not other- 

 wise particularly noticed, always constituted the extra spiral in 

 the experiments with Saxton's machine. I obtained namely a 

 weakening action with certainty only, Avhen solid iron was in- 

 serted ; with other kinds of iron the intensity of the shock re- 

 mained unaltered. I concluded from this therefore, that both extra 

 currents A and E almost completely compensated each other, 

 and that the insertion of iron increases to a nearly equal degree 

 two magnitudes forming a difference. When instead of the 

 two wide spirals I chose one that closely fitted the iron cylin- 

 der, and covered it throughout its whole length, the physio- 

 logical action was then decidedly increased by soft iron, and still 

 more by bundles of iron wires. When this extra spiral was in- 

 serted into a secondary spiral, the shocks from the handles I and 



II on closing the secondary spiral were perceptibly diminished. 

 This increase of power by means of iron even took place when 

 two narrow exti'a spirals were used. For when these Mere in- 

 serted into two secondary spirals connected in a like or in an 

 alternating direction, in the first case the shocks were weaker 

 than in the last, which all tends to confirm the view, that the 

 positive action of E overpowers the negative action of A. If 

 five spirals were inserted an increase in the power of the shock 

 was obtained, as with the connexion II and III, when solid 

 iron was contained in the spirals ; a diminution however was 

 observed when the spirals contained bundles of wires. 



79. Corresponding results to those which have here been ad- 

 duced were obtained when the break was effected by means of 

 the intermittent spring 3), not at an azimuth of 90° but of 45°, or 

 with alternating currents at an azimuth of 45° and 2I5°*. But 



• The cylinder «•,, upon which the intermittent spring 3) slides, can be 

 turned, as can also tr.^ and w^, so tliat this spring can break tlie connexion at any 

 azimuth that is required. This turning is easily effected by filling up the spaces 

 between the cylinders Wj, w^, w'3, w^ with wooden rings round the axis, and 

 pressing them altogether agaiiist the first cylinder, which is fixed, by means of a 

 spring at 15. This spring is not represented at fig. 7, nor are the wooden rings, 



III order that it might be more di.>tinctly seen which cylinders are insulated, and 

 which immediately attached to the axis. If the cylinders cannot be turned, 

 then a sj.ring of a determinate length becomes necessary for every azimuth. 



