Rodolfo Amedeo Lanciani.

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central portion is broken
uj) into a confusion of
minute elevations, which
in the cuts show as dots.
The rings sometimes
seen in this central por-
PbMtlve spark from i/inch balla Striking dia- tion resemble the nega-
tanoe, \ inch. ^y^ figures, and suggest

the idea of oscillations in the discharge
The negative spark gives the figure shown in (4). An ele-
vated ring forms the outer bound-
ary ; inside of this comes a deeply
depressed circle surrounding a cir-
cular disc, whose surface is so ir-
regular that I have not been able
to determine whether it is, on the
whole, above or below the general
V « ^A„,...«" ^®^®^ o^ **i6 V^^^ filj^- Perfectly
''^^^K.SS^^ll'^ ^i^ila^ fS^^, were^ obWd b^

means of the electricity developed
by the Hobs machine, the electophorus and that accumulated
m a Leyden jar.*

Discharge from Pomte.— When a single, instantaneous dis-
charge, from a fine point, falls upon the film, figures similar to
the foregoing, but not so regular, are obtained. If, however,

• In experimenting with a well chargid Lej^n jar, if the eleotrodes D and »
i% 1) are connected with the coatings of the jar, the discharge is so violent as to
perforate the flhn of pitch. Surrounfing the minute perfbration is a drcnlar crack.
Gen«fally the droular fragment thus set free is thrown out, and in the center of
the bright spot of tm expoeed, a minute dot is seen. On examination by a magni-
fler, it will be seen that the tin is fused at this pomt That this is not a thenno-
electrie action of the tin, and htm, is proved by the fact tiiat the fusion takes place
whether the diacha^ge is positive or negative. In using such ajar for the produo-
teon of figures the electrode B should be removed and the sparic thrown on the in-

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292 E. W, Blake, Jr., on a method of producing

the discharge be of negative electricity, and be continued for
a short time, (e. g. during a quarter-revolution of a 20-inch
plate of the ordinary frictional machine,^ the first efiect of de-
veloping is to bring out a star, which mignt readily be mistaken
for the positive figura Inspection shows however that the
rays are not depressed, but devoted. The rays are generally
more or less curved, and resemble the projection on a plane
of the meridians of a hemisphera The plane of projection is
diflFerent in almost every figure. Precisely such a star occurs
in the figure, given below, of the negative spark from the in-
duction coiL

If the discharge from the point be continued for some seconds,
the plate, on developing, snows an infinity of minute circular
depressions with no characteristic distinction between +E and
— E. In developing these plates, especially those charged with
— E, vivid sparks may be seen to rise fix)m the pitch, visible
even in broad day-light

Figures produced by the Induction CoiL

The coil used in these experiments was made at Ruhmkorff 's
establishment in Paria It is capable of giving an 8-inch spark,
but, by reducing the primary current, the striking distance
was brought down to J incn. A single Bunsen's cell was
used, — the carbon being withdrawn so as barely to touch the
nitric acid.


Negative spark fhun term-
inal wires of the induc-
tion oofl.

Positive spark fh>m terminal wires of the
induction ooiL

The positive figure obtained is represented in the aocompany-
ing cut (6). Except its larger size, as compared with fiictional
electricity of the same strikmg distance, there is nothing notice-
able in it

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Figures by Ae Electric Sparh 298

The correspondinff n^ative figure is seen in (7). The cen-
tral star with curved rays, referred to above, is surrounded by
a deeply depressed circle, which is bounded oy a slightly ele-
vated ring. The terminal wires evidently acted here as points,
for the star was not obtained when the discharge took place
from balla

Simultaneous production of the Positive and Negative Figures. —
For this, a plate coated with pitch on both sides is required.
The electrodes D and E (fig. 1) are adjusted at eaual distances
fix)m the upper and lower surface of the plate. Upon connect-
ing D with the prime-conductor the positive sparK falls upon
the upper, while the negative spark leaps up to the lower sur-
face of the plate. Development oy the lamp, without oblitera-
tion of one of the figures, being impossible, the plate may be
heated in an air-bath to about 60°-66*^ C. It is more conven-
ient, however, to throw the discharge upon the plate when warm,
the fibres then appear at once. By using plates of glass, or
mica, mstead of metal, the relative size of the figures is at once
seen. The negative figure is considerably less in diameter than
the positive.* This fact explains why, when +E and — E are
thrown on the same spot, they do not neutralize each other and
the resulting figure is a combination of the two.

An interesting fact, in connection with this subject,, is the
length of time that may elapse between the reception of the
spark by the plates, andf the development of the figure. Sev-
eral plates were charged in immediate succession, and developed,
one oy one, at intervals of two hours. The last, developed
after twelve hours, showed hardly any loss in depth or sharp-
ness, although the weather was damp and unfavorable. Of
another series, the last, developed after sei;en days^ still came
out distinctly.

A charged plate may be breathed upon, and the condensed
moisture be allowed to evaporate, several times, without appar-
ently injuring the latent image. To test the discharging power
of a point, the following experiment was made. One end of
a copper wire was filed to a sharp point ; the other end was
then soldered to a metal plate. This plate had two intersecting
lines scratched on its surface, and was coated with pitch. The
spark having been made to fall on the spot marked out by the
intersection of the lines, (visible through the pitch), the copper
wire was bent over so that its point was directly over the cen-
ter of the latent image and very near it After 12 hours, this
plate, on developing, gave a good figure.

From the manner in which the figures are produced, it would
appear that they are due to the attractions and repulsions of the

* Biess has shown fPogg. Ann., B. Ixix), that the areas of the surfaces occu
pied hj +E and —E or equal quantity, and developed under the same conditions,
areas 7: 1.

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294 J, J, Woodward on the Magnesium and

excited surfeoe.* This seems proved beyond doubt bv the id^-
tity of the Lichtenberg figures, with the depression ^gures pro-
duced on developing. No chemical change of the pitch could
enable it to attract dust

As the point of temperature at which developement b^ins
is considerably below the true fusing point of the pitch, the
work performed by the electricity is no inconsiderable quantity.
Does the electricity dis^pear in performing this work? The
fact that the depression of the surface stops at a certain noint,
while the attraction for the opposite E on the metal plate aliould
be constantly growing stronger, seems to point to an affirmative
answer. As pitch, however, is said to become a conductor when
fused, it may be that the two electricities are gradually trans-
mitted and neutralize each other. Experiments have been un-
dertaken in the hope of obtaining a decisive answer to this
question, but as yet with no result worthy of publication.
Cornell Univ., Ithaca, N. Y., Feb. 6ib, 1870.

Art. XXX. — On ike Magnesium and Electric Lights^ as applied
to Photo-Micrography; by Brevet Lt-CoL J. J. Woodward,
Assistant Surgeon, IJ. & Army. Eeport to Brevet Major
General J. K. Barnes, Surgeon General of the United States
Army, dated Army Medical Museum, Microscopical Section,
January 4, 1870.t

I HAVB the honor to inform you that, on the 25th of October
last, I began to conduct in person a series of experiments, in-
tended to devise means for escaping certain difficulties which
had hitherto prevented the successful preparation of Photo-mi-
crogniphs of specimens, selected fix)m the valuable and daily in-
creasing series of permanently mounted microscopic sections of
normal and pathological tissues, which form so intere^ing a

r^rtion of the treasures of the Museum. In these experiments
used the sun as a source of illumination, and, following the
process which I have described in fiill elsewhere,:j: I had no dif-
nculty in arranging a method, by the aid of which this class of
objects could be photographed ^uite as successftdly and readily
as the diatoms and other test objects which had previously been
so satisfactorily reproduced in this section of tne Museum. I
shall take occasion m the course of a few days to lay before you

* Tlie laws of attraction and repiilBion, for both poaitiTe and negatire ^ectri-
dty being the same, it is not clear to what cause the diflforenoe of the figures i»
to be attributed.

4 Communicated for this Journal by Lieut CoL J. J. Woodward.

I Oinmlar Na 6, War Department, Surgeon 6«oeral*s Office, Nov. 1, 1865^ page
148, flt. Mg. ; this Journal, II, vol xUi, Sept, 1866.

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Hhctric Light8/or Phoii>^micrograj)hy. 295

prints of some of the tissue-preparations thus reproduced. At
present it is my desire to call your attention to certain impor-
tant observations which I had the good fortune to make, wnile
my experiments were in progress, and which it appears to me
cannot &il to be of interest and serrice to all microscopists.

During the last week of October and the first two weeks of
November, I relied whoUy on the sun as the source of illumina-
tion for producing n^atives. In this period, during which I
had but two perfectly cloudless working days, and several frac-
tional dajrs on which my work was continually interrupted by
passing clouds, I had ample opportunity to convince myself
that the uncertainty of the weather was a most serious hin-
drance to the preparation of successful photographs of micro-
scopic objects, and I ceased to wonder that European micro-
scopists, who are exposed to a climate even more variable than
our own, have not yet succeeded in placing the art of Photo-
micrography upon such a basis, as to make a convenient and
habitual auxiharjr in all microscopical investigations. This
desirable end I believe I have attained; but it has been by
resorting to artificial lights and thus making the success of the
process whoUy independent of the weather.

On the 12th of November I commenced a series of experi-
ments with artificial lights which were most fortunately crowned
with success,' both the mamesium and the electric lights prov-
ing adecjuate sources of illumination for the production of
Photo-nucrographs even with the highest powera

For the production of the electric light I used a Duboscq's
lamp, set in motion by a battery of fifty small Groves' elements.
I found that, with this source of light, photographs could be
successfully taken with any power with which pictures can be
taken by sunlight ; and I was delighted to find, as I had anti-
cipated, that the very exaggeration of light and shadow which
has prevented the electric light from being generally adopted
as a source of illumination in the preparation of photographs of
the size of the object, or smaller, proved of immense advantage
in the reproduction of the feeble microscopical images of highly
magnified objects, and that the pictures were hence clearer and
better defined than any photographs of similar objects I had
hitherto seen produced by sunlight I found also that the
electric light was so much more manageable than sunlight as a
source of microscopic illumination, that I coxdd readily arrange
it to produce natives with much shorter exposures than are
indispensable witn the sun.

The magnesium light shared these qualities to a high degree,
but I found that its best work was done when the object was
not to be magnified more than a thousand diameters, and that
there were certain limitations to its use on test objects which
will be referred to in the sequel

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296 J. J. Woodward on the Magnesium and

With one or the other of these artificial lights as a source of
illumination, I have prepared a considerable number of nega-
tives of interesting microscopical objects, of which a few are
appended to this report by way of illustration, while the others
will be laid before you in future reports on special subjects.

The magnesium and electric lights are mentioned as possible
sources of ulumination for the production of Photo-micrographs
by Dr. Lionel Beale, in the 4th edition of his " How to Work
with the Microscope," page 275. I am not aware, however, that
any one has made successfiil negatives with high powers with
either of these lights prior to the experiments here recorded.
There are in the Museum a few photographs with low powers
taken with the magnesium light by Dr. C. F. Crehore, of Bos-
ton, Mass., who kindly presented them August 8, 1866. N^a-
tive No. 90, old Microscopical Series, Army Medical Museum,
represents a few villi from the small intestine of a mouse, pho-
tographed by the electric light with a T*jth objective of Wales
arranged to mamify 84 diameters. The electnc light was pro-
duced by forty Bunsen's cells, and as I had no electric lamp at
the time, I held the carbon points in two retort holders and
managed as best I could, during the exposure, the uncertain
light thus produced. I know of no other Photo-micrographs
than the above to have been actually made by the electric or
the magnesium lights ; certainly if any have been, they have not
been suflftciently successftd for their authors to be willing to
give them any degree of publicity. I have no hesitation, there-
fore, in claiming for the Museum and for myself the credit of
having demonstrated the serviceable character of these lights as
sources of illumination for the preparation of negatives with
high powers, and of having devised a simple method which
brmgs their use within the reach of every microscopist

I propose now to sketch briefly the process by which nega-
tives of microscopic objects can be conveniently produced with
these artificial lignts.

1. The electric light is by far the best of all artificial lights
for the production of photo-micrographs, and, when used as I
am now about to describe, it is both convenient and economicaL
I use a Grove's battery of fifty elements. The battery is j^ced
just outside of the operating room in a closet from which the
fixmes escape through an earthen pipe into the main chimney of
the building. This battery was furnished by Mr. William Ladd,
Nos. 11 and 12, Beck street, Regent street, London, W. The
rubber cups are 4J inches high, 8 J wide and 2 thick. The plati-
nums are b\ inches by 2 J, and weigh about 60 grains each.
The zincs are bent on themselves so as to present a part of their
surface on each side of the platinums, and weigh, when new,
about a pound apiece. Mr. Ladd furnishes these batteries in

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Electric Lights for Photo-micrography. 297

trays of ten elements, at five pounds sterling per tray, and I find
that a battery of five trays is sufficient for most purposes. Seven
pounds and a half of strong commercial nitric acid, and three of
sulphuric, diluted with ten times the quantity of water, is suffi-
cient to charge this battery, which wul then produce the light
continuously for 6x>m three to four hours. The cost of runnmg
the battery for this time, including in the estimate the amount
of zinc consumed, and the cost of amalgamating every third or
fourth time of using, is very moderate. I make it a practice to
have the battery washed out, the acids thrown away and the
porous cups put to soak immediately after I have done the day's
work, ana all this is so simple that I have no difficulty in m-
structing an orderly to do it, so that the management of the bat-
tery does not occupy any part of my time.

The Duboscq's lamp, the microscope and the plate holder are
arranged in a daik room which enables me to dispense with the
use of a camera. The general arrangement of the apparatus is
shown in the cut

The electric lamp of Duboscq (a) is placed on a stool against
the wall at one ena of the room, and its light concentratea by a
pair of condensing lenses (6) on the lower lens of the achromatic
condenser of the microscope. The microscope (c) (a large Powell
and Lealand's stand) is placed on a small table (e) which is so
arranged that it can be lowered or elevated at pleasure and can
be levelled by means of three levelling screws at its base.
The plate holder (^), also arranged so that it can be raised or
lowered at pleasure, is supported by a small table (/) which
stands on three levelling screws. The floor of the apartment is
quite level. The lenses employed for the microscope are those
of Mr. William Wales of Fort Lee, New Jersey, specially
constructed for bringing the actinic rays to a focus. For powers
above the -Jth, however, I have found that the achromatic
objectives of Messrs. Powell and Lealand, of London, answer
an excellent purpose, and indeed that their immersion yV ex-
ceeds in defining powers any objective which has as yet come
under my notice.

In taking photographs with this apparatus, I proceed as fol-
lows : The electric lamp being set in motion, the table holding
the microscope (which has previously been levelled), is raised or
lowered and moved from siae to side till the center of the achro-
matic condenser is brought to the center of the illuminating
pencil proceeding from the lamp ; the object is then placed on
the stage and carefully adjusted A cell of plate glass contain-
ing a saturated solution of the ammonio-sulphate of copper is
fixed just below the achromatic condenser, and not only pre-
vents the admission of non-actinic rays, but excludes the very
great heat which accompanies the electric light, and also mode-

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J. J, Woodward on the Magnesium and

rates its effect upon the eye of the observer. The light thns
produced is very agreeable to the eye, and I find myself able to
work with it from four to five hours without fatigue. It has

also the advantage that all the colors of the object examined
disappear, and the preparation appears black on an azure field
whicn resembles the sky on a clear day, so that the observer

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Ekcbric lAghU/or Photo'^micrography. 299

sees at a glance how the object will apjxear in the photograph
(in which the same black lines or tints wiU be faithniDy repro-
duced on a white field) and is thus enabled to arrange his
achromatic condenser and other adjustments so as to produce
the most satisfiactor^ effect

Every thine havmg been arranged at the microscope to the
satisfSaction oi the observer, the eyepiece is taken out, and the
image allowed to &11 on the ground glass of the plate holder,
which has previously been placed at the distance necessary to
give the magnifying power desired with the objective employed.
The operator adjusts the plate holder to the right height and
sees that it is perpendicular to the optical axis of t£e microscope,
which he readily does by observing that all parts of the field
are equally in K)cus. He then takes out the ground glass and
finishes the fine adjustment with a sheet of plate glass and a
focussing glass, after which the sensitive plate is inserted, the
exposure made and the operation is finished.

To enable the observer to focus the microscope while sitting
at a distance from it at tiie sensitive plate, the following con>
trivance is employed. On the table wnich supports the micro-
scope {e\ two brass shoulders, each two inches mgh, are screwed.
Througn these runs an iron rod nine inches long, on which slips
a brass pulley (cf) which can be clamped at any point A cord
connects this pulley with the wheel of the fine adjustment of
the microscope which is gropved for the purpose. It is evident
that whenever this iron rod is turned, the pulley turning with
it will move the fine adjustment of the microscopa To eflFect
this the iron rod terminates in a souare extremity, so that a
joint of an ordinary fishing rod, to wnich a brass ferrule shaped
like a watch key, has been rivetted, enables the operator to
focus the microscope at anyordinary distance. When greater
distances are required two joints of me rod may be used. The
rod, being graduated into feet and inches, enables the operator to
record the distance employed for each picture. When the focus-
sing is completed, the rod is removed. I have found this simple
and cheap arrangement superior in delicacy and convenience to
any of the more costly arrangements, I have heretofore tried.

The chemical processes, employed in taking the negatives, do
not diflFer in any respect fix)m those used in ordinary photo-
graphic work, and I have found that by employing a practical
photographer, allowing him to manage the dark room and con-
fining my whole attention to the optical arrangements, I not
only get many times more pictures in a day, but they are much
better than can be producea by any one who attempts to do the
photographic work, as well as manage the microscope himself

I find myself thus enabled to sit down quietly of^an evening,
and during four hours work to produce fix)m twelve to thirty

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800 J. J. Woodward on ike Magnesium and

n^atives or more, in accordance with the difficulty of the sub-
jects and my previous knowledge of them. Any microscopist
who is willing to go to the moderate expense of battery and
lamp, and to add two or three specially constructed objectives
to his microscopical api)aratus, can, by employing a photog-
rapher one or two evenings in the month, reproduce all the
more interesting of his month's observations with a degree of
economy and beauty not to be obtained by any other means,
and if he follows the method I have above described, the charac-
ter of his results will be conditioned by his skill as a micros-
copist rather than by any other circumstance. As to the time
of exposure required for taking negatives with the electric light,
I fina that for one thousand diameters about thirty seconds is
necessary for that class of objects, (such as Angulatum, the No-
bert's plate, &a,) for which it is not necessary to employ a
ground glass plate to prevent interference phenomena. In pho-
tographing the soft tissues and many other objects, it is neces-
sary to insert a piece of ground glass below the achromatic
condenser to escape the interference phenomena which else
occur, precisely as must be done in photographing the same ob-
jects by sunlignt This increases the time of exposure to about
three minutes for one thousand diameters. Other powers require
poportional times.

2. The magnesium light affords a beautiful source of illumina-
tion comparable to white cloud illumination of the best charac-
ter, or to the light of the sun after it has passed through a sheet
of ground glass. Without the use of ground glass, this light
serves admirably for the production of photographs of the soft
tissues with any power under a thousana diametera The light
being composed of a mixed pencil, with rays passing in all
directions, there are no interference phenomena, but for the same
reason, on the Nobert*s plate and many test objects, the results
are inferior to those produced by the sun or by the electric
light; with powers much higher than a thousand diameters,
however, the time of exposure becomes inconveniently long.

The process employed by me in the production of negatives
with the magnesium light, is essentially the same as I have
above described for the electric light, simply the magnesium
lamp is substituted for the electric, and the condenser of an or-
dinary oxy-calcium magic lantern is made to concentrate the
light on the achromatic condenser of the microscopa The cut
represents the arrangement The magnesium lamp (a) stands
on a shelf fastened against the wall The condenser (6) concen-
trates the light on the lower lens of the achromatic condenser of
the microscope, (c) which stands on a table (e\ supported on
three levelling screws. The image received on tne plate holder,
{g) which is supported on a table, (/) is photographed precisely

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Electric Lights for PJioto-micrography,


as in the case of the electric light as above described. The
same focussing apparatus (d) is employed and the ammonjo-

solphate cell should invariably be inserted, but the ground

Online LibraryRodolfo Amedeo LancianiThe American journal of science and arts → online text (page 35 of 109)