New-York tribune., 1868-04-29

% Themselves
roun' and SWIM toward the window edge and me o"CE on
follow one after the other In the course OF tWo W
h experiment When repeated gives the same resn,
rheber the drop lies on dark ground, or is hgh'ca
from beneath through tat il IA not the intensity
hnt the direction the rays of light which governs t
movements OF Prof cohn draws conclusions
which may be thus abbreviated: - .,.,oo
ernined by the direction OF the Of light when
falI upon them They are attracted recuhneary by %
.onrce of light Apparent exceptions to this rule are
brought about simply by the form Of the drop OF mass OF
water containing them. -. ~. ,,,oh
10 called the head and that part containing no chorophy
- turned toward tbs light and the green portion ava!
IRON al movements are accompanied by rotation Of
Their bodies around IN the DARK 6ev cam turn from
right TO left or left to right but under ght they have
definite direction which - contrary IN Eueepa, W 10
hands of watch and the same as the rotation Vi lhe
orinents with colored glass show that only the
more refrangibe actnic rays induce this direction
The organisms more strongly attracted by the pi1e
rays while the red are the same as total Darkness
oneha OF the field is lighted by blue and the other ny
red they will go to the blue side, II II be turner
away from the windowedge. There are some exceponai
FORMS which turn away from the OF light by back
ward motion, and afterward return to 1t,
as direction Of movement concerned depend upon the
chemical activity OF these bodies We cam IN fact lnl
tate many Of these movements by purely ehemcal LiU
cesses with the help Of what may be called artificial M
glena, viz fusform fragment OF chalk having % %ohem ~
covered with resnous cement, which, when placed III
diluted sulphurc acid develops chenca aeoh III lls u
covered half and by the backward Impulse hus sene
ated in the direction OF the covered end INC Chalk is
TO rotate.
PERSISTENCE OF VIsIoN--A new scientific toy
hasaely been added the already numerous devices lo
re bent To Coincide with the outline Of oneha Of
decanter vase, or cup, which, when attaehe 70 r
rg lives view Of the whole object intended to be
shown. This phenomenon depends upon th2 Iate 20
a lie instant the rays reflected from II have ceased to
enter the eye 1t is accounted for very clearly ey INC
tno nfH HQht
many other Instances that the organ aGtGd % brn gp9
by yibratory force Is, ltseli sc. % iHso 'iDt% nar
ceptlon continues about oneeighth OF secoha
after the actual a tnD 0 dn1 IS pTeyen
the eye from detecting its absence IL Is Therefore % o ~
TO revove the wire ot inc 10Y a auea LII I'M h @
shown eight times per second IN other WOrus, eRn'
revolutions OF the wire within second VIII gG XIV frrnd ~"
that the parts the axis, revolving so nueh soWer
than those most distant nom IT, would no, pe hS % 5
actual distance made by the wire In space the slmpo
requisite being that every part Gf the oe ~ s
seems very short yet the actual number OF Vibrations
TO- ote the incredniiiy OF those who have not fully in
vestigated the subject The most common case OF per
ssence is the line Of light which boys at play sometimes
produce by rapidly rotating hrebTand. The same eject
Z seen in the ight Of rocket and grander scale In
'H wte spot on dark wheel revolving at high speed
p0rtrays white ring and spots OF different cooTs VIII
Se made by mixing similarly coorcd paints One OF tho
most curious optical illusions il presented when rada
lines on dlerent revolving discs assume the form OF
curves. -,,, ,,-...., /, -,
Persistence Of vision can he most readily Illustrated by
drawing the upper half OF the human face or form on one
side of a small card, and the lower half Immediately un-
derneat but opposite side OF the card ana thc
suspendlng from tho top by thread so that II VIII
hang i'm a vertical line After twisting the thread SUM
ceny arapd rotation OF the card ~ is lett I,ee
10 move and when the two halves are each presented
TO the eight times second their images become
combined tho retnn, and form complete picture
Various plans for producing the sae elect VIII douDess
be suggested 10 the reader. - -,,-, -
There is another class OF visual Impressions which are
reproduced nyOuntaly when the eyes oVertasked Inc
reiina generally dclcatey constructed as 10 Dc sen
sve 10 many hundred different tints, and 10 responds 70
the unduatOns causing them a. o convey 10 the hd
distinct impression Of each. When however the retlna
isexposcd to the direct rays OF strong lght-tho sum-
for instance-t is thrown into such violent internal ag
taton that brilliant image 0f the object from which tho
gI en- anaed will he visible for several minutes when
the oyeds are closed and viii sometimes Teappear IN dl
vcrsffled coors, which generally complimentary 70
those Immediately preceding remarkable pecunarlty
In these phenomena the roappearaDce OF the latent
image which may even be recalled or reproduced ny an
act OF tile will after the has received many other l
prcssOns I Ia not improbable that the spectral appar
lions which formerly said 10 haunt humanity In the
wtching time Of night were the offspring Of dloI-
dcred and ovoTcxcied retina thus every imphlpabe
shape that naturally the remembrance OF IT'D
original when conjuTed by diseased Imagination, be
came to 4" the minds eye" a terrible realty.