196 Dr. Faraday’s Experimental Researches in Electricity. 
on to the galvanometer is a maximum ; if the commutator change 
at the moments of maximum velocity, or at any other pair of 
moments smaaine from the one — or the other, then the cur- 
rent at the commutator is a minimum, 
» 2669. There are two or three scent which are necessary 
to the production of a pure result of this kind. In the first place, 
the iron ought to be soft and not previously in a magnetic state. 
_ In thenext, an effect of the following kind has to be guarded 
against. i the iron core be away from the dominant magnet at 
4 the beginning of an experiment, then, on working the machine, 
ah the a ispeanensee wilk:be seen to move in one direction for a few 
; moments, and afterwards, notwithstanding the continued action 
the machine, will return and gradually take up its place at 0°. 
Tf the iron core be at its shortest distance from the dominant 
- ‘Magnet at the beginning of the experiment, then the galvanom- 
eter needle will move in the contrary direction to that which it 
“took before; but will again settle at 0°. These effects are due to 
"the circumstance, that, when the iron is away from the dominant 
“~-" magnet, it.is’not in so strong a magnetic state, and when at the 
. Reatest to it is in a stronger state, than the mean or average state, 
which it acquires during the continuance of an experiment ; and 
tS ers in rising or falling to this average state, it produces two cur- 
“re its in contrary directions, which are made manifest in the ex- 
e ments described. These existing only for the first moments, 
‘<. do, in their effects at the a then appear, producing a 
% aetioe ampich gradually passes a 
, . other precaution I at to specify. Unless the 
Sonnets er nges accurately at the given points of the jour- 
‘ wey a si effect is gathered up at each change, and may give 
if defleetion of the needle in one direction or the others 
3 Phe ‘one of my commutator, being at right angles to the di- 
i» + recti nedf. mhotion-and somewhat. flexible, dragged a little in the 
my to and from par ts of the journey: in doing this devi peeeeets 
get ouly. in a small degree, to that which is the best,con ndi- » 
f the, rl x for gathering, up pe not opposi 
ah of abd: rig tor 
* 
gent be 
pl aed, mi terre t le t disap 
ecily igact .! 
i267 
sucht therefore are. with? ait : 
> the'effects’ with a @f ot. bis Bie sore if ‘they 
de yee toa, , 
waver to act, j 
iced for the “tifne" may fhe’, ” 
of those suspected (2642.).” ee moved oa 
the exist 10 _ a 
de —— A Tae Aes 
