New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1872-12-23

In the diagram, Is the lantern containing the eecuo
light b plain mirror the lens with magnets above
it; n rght-angled prism detecting the ray toward tho
screen.l
THE LECTURE.
In orr last lecture we sought famlarzc our minds
with the characteristics OF wavemOton. We drew
clear distinction between tho motion Of the wave itself
and the motion Of its constituent particles. Passing
through waterwaves and air-wayes we prepared cur
minds for the conception Of light prUpagaeed through
tine luminferous ether. Tie analogy OF sound
will fix the whole mechanism in your minds. Here VIC
have vibraory body which originates the wave-moton
we have. in the air vehicle which conveys It, and We
have the auditory nerve which receives the
impressions OF the waves In the case 81
light we have In the vibrating atoms Of the lumi-
body the orGnators of the wavemotion, we have
in the ether its vehicle while tho optic receives
the impression Of the lumniferOus waves. We learned
Also that color the analogue OF pitch that tho
rapidly atomic vibration augmented aud the length
OF the ether-waves decreased passing FRO the red
TO the blue end Of the spectrum. The fruitful principle
Of interference we also found applicable 10 the phe-
nomena OF light and learned that IN consequence OF
tho different lengths ofthe ethergayes, they were eN
ngushed by different thclnesses OF transparent films,
the particular thickness which quenched one color glow
ing with the complementary ones Thus the eolors OF
thin plates were accounted FOR.
PHYSICAL ORIGIN OF SCIENTIFIC coScErrioSs.
But Of the objects OF last lecture and thn not
the least important, to illustrate the manner IN
which scientific theories formed. They. IN the rst
place. take their rise desire of the mind TO pene-
rae 20 the Of phenomena The desire has long
been part Of human nature. 1t prompted Cesar to
say that he would exchange his victories for glimpse
Of the sources of the Nile it may be seen working In
Lncretus; it impes Darwin to those daring speona-
tiOns which Of late years have so agtacu inc Phbo
mind We have learned that in framing theories ihe
IMAGINATION does not create but that it expands dnn-
derived from the world of fact and observation.
This is more evidently the in theory ike that on
ether are presented to the mind But theory escapes
the condition. Newton took tcare not to ineamDet
gravitaon with unnecessary physical conceptlons but
we have reason TO know that he INDUCED N them,
though he did not connect them with ms theory bt
revelation discovered from the world OF oct Inc germ
of the conception that the sun ana n5 ff IN tbe
fact that magnet had been previously seen TO attract
iron. The notion OF matter attracting matter came nus
from without not from within In our present Lecture
the magnet force must serve us still further but here
we must master its elementary phenomena.
NOTIONS ATOMIC POLARITY DERIVED FROM THE MAC
NET
The general facts OF magnetism ore most simply Illus
trated by magnetized bar Of steel, commonly called
bar magnet Placing such magnet upright upon Ia
ble and bringing magnetic needle near its bottom one
end Of the needle promptly retreats from the magnet
while the other promptly approaches. The needle -
held auiyerng there by some invisible influence exercd
upon IL. Raising the needle along the magnet but s
because the force upon the needle becomes
weaker At the center the oscillations cease ABOVE
ward the magnet retreats. and the opposite end APP
proaches AS ascend higher, the osciatons oecome
the upper end Of the magnet at the lower The force
reaches maximum but all the lower nall OF ,ae mag
net attracts one end OF the needle, while all the upper
half attracts the opposite end This doubeness OF tho
magnetic force is called polarity anu the ponls near
the the magnet In which the forces seem concen-
trated are called Its poles
This was very clearly shown with bar magnet two or
three feet in length. The poles of the needle carried
Gags making It's movements APPARENT
AZ in fvrn
az the cener Will each of the separate halves act it
did when IL formed part Of the who pagnett No;
S pcss hN hi. m % proved By Sressns
less value than the msgnet-the steel Of sdys stays
magnet. When broken, each half acts like the whole;
and when par as n the , Instance
two poles Push your breaking TO its utmost Limit you
spd to to Contemplate this thing that we call magnetic
polarity resident In the ultimate particles OF tho
magnet Each atom is endowed with this polar force.
TENDENCY OF NAoNETizED PARrrcLEs TO ASSUME p8FI-
MITE FORKS.
Like all other forces this force or magnetism Ia amen
able TO mechanical laws and knowing the direction and
magnitude OF the predict Its action Piac
ing small magnetic needle near bar magnet. IL takes
up determinate position. That position might be do
Moving tie Needle round the magnet for each pont Of
the surrounding space rs definite DIRECTION OF the
well as the mssnetio noede for Inc needle q iron Is
magnetir.d BY the magnet and act: s1Sstiy like .
moro rods q iron near the magnet the action becomes
more complex for then the iron needles are not only
And we pass to smaller q iron nss.
for eIAmpiewe ind that they act substantially a. tho
9eedes ARRANGING tasmssves ID dsnn''e 'orm1' IN ooe'
Pses this bar m.sns.
tendency Of the anss to Arrange in deter.
nnatc inss They cannot freely follow this tendency.
sAs% ios s's% sns sS.ss: s sa' . iSss Ss