M'GAULEY ON ELECTRO MAGNETISM. 
531 
helex cannot be unlimited, as, beyond a 
certain distance from the iron, its action 
is nothing,— in some cases, perhaps, as 
we shall see, even injurious. The effec- 
tive distance of the helex from the iron 
cannot be great, since its action, 
})robably, decreased in the inverse pro- 
portion of the square of that distance. 
The difficulty cannot be obviated, as 
some have imagined, by causing the 
electrical currents to circulate through 
the mass of iron, uniting together a 
number of coiled bars. This would 
present an arrangement probably similar 
to a permanent magnet, the masses of 
iron acting on each other by induction, 
the reversion of the poles would be 
very slow, or altogether impossible. 
The action of the magnets, rather than 
their masses, must be united; but in 
this, new difficulties occur. Their action 
must be simultaneous, or the machine- 
ry will be broken, or ineffective ; the 
time after reversion, and during which 
a har can be thrown off a magnet, is 
extremely short — hence one reason why 
it is difficult to unite the action of 
several magnets. But let us suppose 
that we have obtained a simultaneous 
reversion of the poles and throwing off 
x)f the bars — a thing totally impossible, 
he conceived, from the number and 
complication of circumstances by which 
it is influenced — how shall this action 
be applied to machinery? If the fly- 
wheel of a steam-engine, from the shut- 
ting off of the steam, be not impelled 
by the engine while it continues in 
motion, it drags the piston, uninjured, 
through the cylinder ; but suppose 
something to retain the piston in one 
position, without stopping the wheel, 
the effect were highly injurious — this 
is exactly what must frequently happen 
in electro-manegetism. It is impossi- 
ble to reverse the poles even of one 
magnet, in such a manner that the 
position of the bars shall always corres- 
pond with the position of the crank and 
fly-wheel.* 
Let M m’ be two magnets, m m’ be 
the space through which b, the bar, 
travels in causing half the revolutions 
of the crank c’ x, while b is moving, 
so that its extremity shall be at p’ 
then c’ X shall have become c’ x’ 
while it is going to p”, c’ x’ shall be- 
come c’ x’” but if when the crank c’ x 
is in the position c’ x’” one of the 
dead points, the bar is not ready to leave 
m’ ; or, in other words, if the magnet 
which holds it be not ready at once to 
send it off — a thing very probable — the 
fly-wheel continues to revolve by its own 
inertia, and the machinery is broken, or 
the bar is torn from the magnet, which 
offen has a curious and perj)lexing ef- 
fect on the reversion of the poles. 
A better reversing apparatus was to 
be obtained.* 
Again, the form of the apparatus, 
whether mercury be used or not, must 
be changed, and the principle of the one 
now exhibited to the Section adopted, 
since the apparatus, which will reverse 
the poles of one magnet, will not with 
speed of certainty reverse the poles of 
two or more, when worked by the en- 
gine itself. The apparatus shown to the 
Section had been used with great suc- 
cess in (he reversion of the poles of four 
powerful magnets. 
The attachment of the reversing ap- 
paratus to the machine becomes difficult, 
when more than one magnet is used, for 
reasons with which he would not then 
occupy the Section. He believed he 
might mention, that he possessed an en- 
gine of considerable power, in which 
these difficulties were overcome. 
The e.xperiments he should detail to 
the Section were numerous and compli- 
cated ; he had taken ev^’ery means to 
secure their accuracy ; some of them ap- 
pear anomalous, but were undoubtedly 
modified by circumstances, many of 
which are so obscure, that he has not 
been able yet to detect them. He re- 
marked, that it was obviously important 
to make experiments in considerable 
number, and on a large scale, since the 
former secures a greater accuracy, the 
latter the notice of results which, from 
their minuteness, might otherwise es- 
cape observation. His inquiries resolved 
themselves into two points — the nature 
of magnetism — the best means of pro- 
ducing it. The means of overcoming 
the difficulty arising from the necessari- 
ly limited size of the iron and the helix, 
he might probably treat at a future pe- 
riod- 
To place everything in exactly the 
same circumstances, without which a 
fair comparison could not be made, the 
battery was cleaned, the charge renew- 
Sfle plate iv. fig 6. 
* See Plate iv. fig 1 
