New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1868-11-26

OF the curvature of the field and the distortion OF the
image Though the lenses only are required In order
that we may state the principle OF the in9ttumeht num-
Der necessary for the purpose Oh aecns aho
oBs just mentioned: In the hrst place tl9 %
arc much reduced by employing, Instead OF single
raons increase rapidly with curvature Three lenses OF
low curvature will have much less than slnge one
ect Waved is placed within the principal focus OF the
rst OF the three forming the combination me negalYe
falls within its principal focus also. second negative
image thus produced falls Without the principal FOCUS OF
IMAGE 70 he observed by tho eye glass Another very Ina
portant end is attained by making the obeetgiass com
alterations of sphercity the correction VIII pc G0ou
only for certain distances OF the object IRON se
will be aplanatic without aberration II the oDlece
D pc pt the alteration win bo oyercorretod the
foci OF marginal rays VIII be too long and those OF s1ai
& lens than the moro remote OF points, or less
distant than tho least remote the alteration VIII De
nndercorrected In the compound objecgass the lenses
are 90 naced that when the object is in the short apena
tic focus OF tho first glass; the negative image 10 IN Wy
longer apanatc focus Of the second and third eonsd
sred M one and tho alteration is suppressed But
more important fact IT, that the obque rays LOT WINCH
tbe berration as already stated Is not corrected with
az SINGLE lens il such as to produce two opposite and
cOuperacng effects In the two points JUST henonou
these obilGue pencils OF rays throwing luminous coma
m tho longer focus and similar coma inward
nj the shorter The two enects Daahce anu uhus tno
compound objective produces an image free rom aDeIa
tnn throughout Another advantage IS secured by the
compound objective. When the object IS viewed rosn
n glass cover even though the cover be not more tan
the ono hnndredth or One-twO hundredth OF an lheh
thick the pencils coming from 1t arc mace, las aas
earlier been stated abeant The alteration pro1ucea -
nerstiye II the front lens be slightly wltnunaWn, he
others remaining stationary, the object WIZ ian lutO Inn
space between the two aPlanauc iocli III WIZ
tho alteration produced is positive the two eneGs
counterbalance each other rud tne pereclGn VI he
image s moro restored. Inc c9rIsct n2
described founded on discoveries MADE by Mr. y %,
Lister of London and communicates 10 'ne n1g and
eety I'm 1890 They gave 70 the lhsIuhlent a
perfection previously unknown, ana cOnsLtu1e tc os
tal feature OF all modern hrstcnss GuJec.ges' ~
though alterations thus corrected inc curyalue
the image remains % DO removed ms u accVn
by invoking the aid OF the eye.gasS or, as II - nOto
pod as well ns the objective. 1t consists essentially OF
two planocouyex lenses the smaller nearest te ~
6ss be e uo Which Il Was originally designed to subserye
the field glass. 10 bends the pencils preceding IS
object glass inward as Is seen on the olss n ne
be eve better command OF Them IL thus enaIges tne
field OF view, though reducing some"nat az sAo onb
time the size OF the image But u ,d b,,
moro important object than this. The image 1orsu Dy
the rays from the oeetgass Is seen ~ b De "a be most
unfay0rabe position In when 10 view ~, sinCe .i'o
eyegass itself tends to produce eonye1y pa even
fiat object In the same direction But t1 nS tbev
ceyng tho rays OF the c0nvergng pencils OeloIe my
reach their focus sends them 70 an9'e u s are IN
where tho curvature Is reversed Inc wv ~. ~ ~
fact corjugate but one Is neg9uye % Ine o,net I'D
image thus formed by the Hsasa, n5 NE c"n
the eve; and this IS the KIND OF image 70 when Ie @
gate through the eyogass nat OF ICES r3uuer VI
rounded the other way IL cyatures n tSe several
glasses which shall produce exactly the Mattress OF neu
des ccts %, this admirable combination. Tho oye
glasses may produce color as wei Is inc oDleS,
e0uire unnecessary trouble and expense since inc same
sgict may be produced in another mode, which viii
en- That Is TO say tho blue image Of the corrected
glass Is formed further from tho lens man INC reu
diagram before shows the relative positions OF tne
two images. These two images are & aPproS
which, being uncorrocted, acts more poWerI9y on VIC
blue than on the red Ths margns Of me Two
through tie center OF the eyegass. which axes are the
hundars OF tie negative resultant image finally seen
D.
class more powerfully upon tie blue than upon he req,
6ngs 5oin ~ f ayesed Of ali tts perfectons it is
without alteration, without dslOrloh' NllNoal oooi -u
Those results areTnot by any means secured with the
facility with which speak Of them here Tie utmost
dracy is necessary In the adjustment OF the several
parts; tho careful computations are indispensable
ior tie determination Of each curvature and nnaly'
the most exquisite artistic SKIN must De !ad 'e5 Co
trbution 20 realize In execution the e1aeons OF tho0
II any production OF the combined resources OF OK. ana
an eminent degree the modern perfected microscope
The question sometimes asAed, m'at +, ~
be answered that miseroscope should be chosen WIN
reference TO the purpose 70 when 20 ~
valuable Sny purpose, and that Is what is called
OF the outlines Of the objects obseryed Great OF
enlargement seems TO % supposed 10y many 20 ps oe
no magGlfyng power OF any value, Tor definition u
Grat msnifying power Is indeed many purposes
dsadyantage rather than the contrary To SEQ an object
IN Whole or ny Re .RSgd be o% AND
n slould always be remembered that when the
apt Ia see 10 Increase IL would be than useless
The field on the stage commanded by powerof one
inch in diameter. With power OF one or two thou
sand puucture of me needle Ia card would more
Than represent the entire space which the observer could
single view. Hence except Tor inc very mnutest
objects hiE powers STF means FORMS and Outlines De-
filming power being secured We need next either
Re1e'ts'I he uses uses we expect 70 make Of tho
instrument BY penetrating power Is meant certain
command OF the parts OF the object which are above or
below the plane OF the true FOCUS li9 tne 90 :
itself possesses IN al eminent degree ~ FURNISHES us
notions OF the relations OF parts TO each other which can
true focus IS utterly confused. Penetrating power can
the magnifylng power Is low. Resolving pOwers name
for the gree OF efficiency Of the Instrument In separa
the Object observed rms quahy Is only secured 10y
making what Is called the angular aperture
the objective aS Large dno s pRsSd w aPs
can be given the pencil OF rays which the objective
that the minute tacery upon tho surface OK an object
is made most conspicuous The reason OF this VIII easily
appear from the diagram exhibited. The relative dis
thickness of such markings as shown the scale OF
butterys wing this other figure with different angles
Resolving power and penetrating power are, for obvious
reasons, certain extent antagonstc 10 each other
Hence both are not TO DO sought Tor III the same oo
The lecturer then proceeded 10 exhibit and explain diff
ferent forms Of the microscope. the ordinary compound
microscope the bnocuar microscope tho inverted mi
oroscope for chemical purposes, the double triple
microscope &c; after which he spoke Of the modes o
illumination, and described number OF forms OF acces
sorry apparatus together with the modes OF measuring
the dimensions OF microscopic objects aud OF determining
magnifying powers lie referred also TO the wonderful
perfection OF mechanical art IN recent times illustrated
| In microscopic ruling aud engraving, and mentioned
Noberts plates which the finest Ines 100 600 10 the
Paris nch have never been rs yet fairly resolved prs
Curtis and Woodward, OF made ENLARGED
photographs Of these lines hgh $4,000 To tho Pan
nch or than 10000 TO the Eugsh inch. He SPOKE
also Of an engraving executed for him last year by Du
moulin Fromen OF Paris representing the seal OF Coumbs
Collage with all It's pictorial devices, and its notices