180 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXllI.) 
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 midway 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 88] 12, gave the best result with a copper core. On the whole, and after 
many experiments, 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, 86ll4 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. Flence the power of submitting by this 
machine metals and other bodies to experiment, and of eliminating the effects of mag- 
netic 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 sepa- 
rated ; and further, they can also be combined 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 tt, h or c, d, &c. the periods in the journey when 
the commutator changes (in which case c, d will cor- 
respond to 60|50, and e, f to 86|14), then a, h will 
represent the condition of the commutator for the 
maximum effect of iron or any other polar body. If the line a, h be gradually re- 
volved until parallel to c, d, it will in every position indicate points of commutator 
change, which will give the iron effect at the galvanometer by a deflection of the 
needle always in the same direction; it is only when the ends a and h have passed 
the points c and d, either above or below, that the direction of the deflection will 
change for iron. But the line a, b indicates those points for the commutator with 
which no effect will be produced on the galvanometer by the induction of cm^rents 
in the mass of the core. If the line be inclined in one direction, as /, A-, then these 
currents will produce a deflection at the galvanometer on one side; if it be inclined 
in the other direction, as /, m, then the deflection will be on the other side. There- 
fore the effects of these induced currents may be either combined with, or opposed 
to, the effects of a polarity, whether it be magnetic or diamagnetic. 
2678. All the metals before mentioned (2655.), namely, gold, silver, copper, tin, lead, 
platina, antimony and bismuth, were submitted to the power of the electro-magnet 
under the best adjustment (2675.) of the commutator. The effects were stronger 
