supposed Polarity of Diamagnetic Bodies. 99 



would commence at those points of the journey ; but, as the 

 core is entering into a more intense part of the field, the cur- 

 rent in it still rises though the velocity diminishes, and the 

 consequence is, that the maximum current in it neither occurs 

 at the place of greatest velocity, nor of greatest force, but at 

 a point between the two. This is true both as regards the 

 approach and the recession of the core, the two maxima of 

 the currents occurring at points equidistant from the place of 

 rest near the dominant magnet. 



2674. It is therefore at these two points that the commu- 

 tator should change, if adjusted to produce the greatest effect 

 at the galvanometer by the currents excited in the experi- 

 mental helix, through the influence of, or in connexion with, 

 currents of induction produced in the core ; and experiment 

 fully justifies this conclusion. If the length of the journey 

 from the stop out to the stop in, which is 2 inches (2643. 

 2644.), be divided into 100 parts, and the dominant magnet 

 be supposed to be on the right-hand, then such an expression 

 as the following, 50|50, may represent the place where the 

 commutator changes, which in this illustration would be mid- 

 way in the to and from motion, or at the places of greatest 

 velocity. 



2675. Upon trial of various adjustments of the commutator, 

 I have found that from 77[23 to 88J12, gave the best result 

 with a copper core. On the whole, and after many experi- 

 ments, I conclude that with the given strength of electro- 

 magnet, distance of the experimental core when at the nearest 

 from the magnet, length of the whole journey, and average 

 velocity of the machine, 86|14 may represent the points where 

 the induced currents in the core are at a maximum and where 

 the commutator ought to change. 



2676. From what has been said before (2667.)? it will be 

 seen that both in theory and experiment these are the points 

 in which the effect of any polarity, magnetic or diamagnetic, 

 would be absolutely nothing. Hence the power of submitting 

 by this machine metals and other bodies to experiment, and 

 of eliminating the effects of magnetic polarity, of diamagnetic 

 polarity, and of inductive action, the one from the others: for 

 either by the commutator or by the direction of the polarity, 

 they can be separated ; and further, they can also be com- 

 bined in various ways for the purpose of elucidating their 

 joint and separate action. 



2677. For let the arrows in the diagram represent the to and 

 from journey, and the intersections of the lines a 9 b or c, d, &c. 

 the periods in the journey when the commutator changes (in 

 which case c, d will correspond to 50|50, and e, t fto 86|14), 

 then «, b will represent the condition of the commutator for 



H2 



