Memoir of Joseph Zentmayer
From the Journal of the Franklin Institute, Dec. 1888
JOSEPH ZENTMAYER, optician, whose name was known all
over the world, and whose death is so sincerely deplored by
all his fellow-members of the FRANKLIN INSTITUTE, was born
in Mannheim, Baden, in South Germany, in 1826. He
received a good education, and learned his trade as an
instrument maker. At the termination of his apprentice
ship, and after having made his "masterpiece," as is the
custom among German mechanics, he travelled throughout
Germany, working in the best establishments, and improving himself in the knowledge and use of scientific instru
ments. He was an ardent republican, and his natural love
of liberty led him to take an active part in the agitation that
had as its object the establishment of republican institutions in Germany.
came to America in 1848, in the 24th year of his age,
hoping to find a free scope for his notions of freedom in the
western Republic. Between 1848 and 1853, he worked for
the best instrument makers in Baltimore, Washington, and
in Philadelphia. In 1853, he began to make mathematical
instruments in Philadelphia, at Eighth and Chestnut Streets,
with but one single lathe. The high character of his work,
and the boldness of his conceptions, attracted the attention
of the leading scientific men. Among these, the late Dr.
Paul B. Goddard was particularly drawn to him, and it was
Dr. Goddard who persuaded him to make the first of his
large compound microscopes. This early effort was so successful that the Academy of Natural Sciences, and many of
the leading physicians who required such instruments, purchased those of his make and discarded the heavy and yet
unstable instruments of European manufacture. Once fully
embarked in this enterprise it seemed to absorb his whole
attention, and many were the improvements that followed
each other in rapid succession, not only in the stand of the
microscope, but in its objectives. At the present time,
there is not a maker of microscopes in the world, who does
not use some of the important inventions of this Philadelphia mechanician. During the war for the Union he furnished most of the microscopes used in the Government
hospitals, and he received the highest commendation from
all the officers and other authorities for his work.
The Chairman of this Committee made the acquaintance
of JOSEPH ZENTMAYER in 1861, and from that time until
shortly before his final illness, enjoyed the most intimate
and agreeable relations with him, of a social, scientific and
During these many years Mr. ZENTMAYER devised and
constructed a great variety of apparatus, which was used in
researches or in the illustration of lectures.
The success of these researches and the effective illustration of these lectures, were largely due to the ingenuity and
genius of Mr. ZENTMAYER in devising, and to his accuracy
and delicacy of workmanship in executing this apparatus.
Accounts of the structure and operation of some of these
pieces of apparatus will be found in the JOURNAL OF THE
FRANKLIN INSTITUTE, 1865, VOL. 79, p. 421; 1866, VOL. 82, p. 66:
1867, vol. 83, p. 406; 1868, vol. 85, pp. 64, 207,345. Also
in the Philadelphia Photographer, 1867, vol. 4, p. 218, p. 231.
In many instances portions of this apparatus had to be
ready at short notice, as in the case of some lectures at the
Academy of Music, and their completion involved special
exertion and prolonged hours of work. In all such cases
Mr. ZENTMAYER'Swillingness and enthusiasm were of a
character which should never be forgotten.
His interest and anxiety for the success of the experiment seemed fully equal to those of the lecturer himself.
In 1865, he invented his photographic lens. The story of
his invention of this photographic objective is very interesting. At the time when the Harrison globe lens was attract-
ing attention one member of this committee, Prof. Coleman
Sellers, was requested to write a paper for the American
Journal of Science and Arts on the nature and advantages of
the globe lens for the photographic camera. After this was
published, its writer consulted Mr. ZENTMAYER. about the
combination, and he said that it was quite possible to make
a lens of two simple uncorrected concavo-convex or meniscus
glasses, made thin and of proper curves, and that such a lens
would be chemically correct as to focus, and would also copy
a drawing with the marginal lines straight, that is, without
any bending of the lines either out or in. He was urged to
make a lens of this kind, and finally he did so, sending it to
Prof. Sellers to test. That first lens, made as he had proposed, was perfect in its definition, and had all the good
qualities he had promised. Most lenses for this kind of work
have been the result of a long series of experiments ending
in the form adopted. In this case a lens constructed upon a
theory proved the correctness of that theory in a most
remarkable manner. The Zentmayer lens, which in working is as rapid, if not more so, than other globe lenses in the
market, was more simple and filled a want, inasmuch as his
system enabled him to make a series of lenses, the front of
one lens being used as the back one of another through a
series of sizes from the longest focus wanted to the shortest;
a set of these lenses, combined as required, meeting all cases
that could occur both as to size of plate and proportion of
reduction. Mr. ZENTMAYER's patent for these lenses was not
granted at once, but he was obliged to contest his claim
before a master, in which examination his claim in regard
to priority was fully sustained.
At first Mr. ZENTMAYER objected to patenting this lens,
and it was only at the urgent solicitation of Prof. Sellers
that he finally consented to do so. Much controversy
resulted from the introduction of this objective, but it
established Mr. ZENTMAYER's reputation as a photographic
optician of the first rank.
So radically original was the invention embodied in this
lens, that the descriptions of it were at first regarded by the
practical opticians of Europe as incredible and as American
exaggerations, and these ideas led to quite an animated
controversy, which may be found in the JOURNAL OF THE
FRANKLIN INSTITUTE, 1867, vol. 83, p. 349; also, 1868, vol.
85, p. 153, and more fully in the Philadelphia Photographer,
1867, vol. 4, pp. 177, 251, 253, 344; also, 1868, vol. 5, pp. 79,
This lens was first described in the JOURNAL OF THE
FRANKLIN INSTITUTE, 1867, vol. 82, p. 63, and reports on its
performance by a Committee of the Photographic Society of
Philadelphia were published in the Philadelphia Photographer, 1867', pp. 44, 151.
When, in 1869, the Chairman of this Committee organ-
ized the party to make photographic observations of the
total solar eclipse visible in Iowa on the 7th of August, Mr.
ZENTMAYERdevised and constructed the special photo-
graphic lenses which replaced the eye-pieces, and also the
drop-shutter attachments for regulating the times of exposure, used with the equatorial telescopes employed on
During the preliminary rehearsals and experiments in
West Philadelphia, where a temporary observatory was constructed and two of the equatorials were set up, adjusted
and operated in making photographs of the sun and moon,
Mr. ZENTMAYER was indefatigable in assisting the work, day
and night. He also joined the party and went with it to
Ottumwa, la., where his knowledge and fertility in resources
to meet unexpected difficulties contributed largely to the
success achieved by that section of the party. All this personal work at Philadelphia and in Iowa was a voluntary,
gratuitous, contribution. A description of the above-mentioned apparatus and of the work done with it will be found
in the JOURNAL of THE FRANKLIN INSTITUTE, 1869, vol. 88,
pp. 200 to 2l6, Les Mondes, v. 21, p. 228; also in the Philadelphia Photographer, 1869, vol. 6, p. 305; also in the Reports
of the Observations (of the Total Eclipse of the Sun, August 7th,
1869), published by authority of the Secretary of the Navy,
After the system of screw-threads, known as the "United
States," or the "FRANKLIN INSTITUTE, Standard System of
Screw-Threads" was introduced, and makers called for instruments to measure the amount of reduction or the width of
the flat top and bottom of the threads, a set of thin steel
plates ground to an angle of 60 deg was sent to Mr. ZENTMAYER
to have him grind the apex of each to the proper amount.
The width of each being given to him in decimals of an
inch to the fourth point. In topping these off he measured
the flat by means of a stage and eye-piece micrometer. The
correctness of his work was then verified by a member of
this Committee, who, taking the finished pieces, measured
them on his own microscope in the same manner, setting
down the dimensions as found, and afterwards comparing
them with what was required, with the result of finding
them correct to the fourth place of decimals in each case.
This was, in the first place, one of the earliest instances in
which the microscope was used in such amechanical pro-
cess, and a remarkable example of the facility with which
good instruments can be used in such work of precision.
The standard gauges, made since by the Brown & Sharpe
Manufacturing Company, have all been adjusted to the
standard pieces prepared by Mr. ZENTMAYER.
The wonderful comparator, designed by Prof. Rogers, of
Boston, and made and used by the Pratt & Whitney Company,
of Hartford, Conn., is furnished with microscopes made by
Mr. ZENTMAYER, who took great pains to perfect the instruments to be applied to this system of comparing measure-
ments. In all cases where work of great nicety has been
required, those who knew Mr. ZENTMAYER'S skill were in the
habit of seeking his aid, even in matters not pertaining to
optics. The freedom from petty jealousy that marked his
character was pleasing to his many friends. No one ever
heard him say a harsh word about rivals in trade, even
when in the contests, called by some sharpness in trade, he
might justly blame some for having acted unfairly. Those
who have been for years in the habit of visiting him in his
shop, know how kind he always was and how patiently he
listened to what they had to say, giving freely from his great
store of knowledge, showing his methods and even supplying to those who wished to make any piece of apparatus
themselves such parts as he could find suited to their
Mr. ZENTMAYER'S office in Walnut Street, where he had
his lathe close to his counter and near to the cases contain-
ing his instruments, was the meeting place of all the
scientists of the day. There, at all times, while he was working, professors and physicians and mechanical engineers
would meet and discuss problems in optics or in mechanism;
all of these men learning to love the good man who was so
simple-minded, and so honest in his dealings. Many times
young men, coming to purchase their first microscope, found
the great optician advising the purchase of a good working
instrument, cheaper than the one they had come to buy, but
well fitted to do what would be required of it. No instrument would leave his hands without being personally
inspected by him, after he had advanced to the condition of
employing workmen to do what at first he did with his own
hands. All those who knew Mr. ZENTMAYER felt the influence of his honest, straightforward seeking after truth. It
was always a source of pride to him that among the many
thousand instruments which he constructed, none ever came
back for repair after years of hard usage, except in the case
of severe accident, such as would come from a fall, or the
like. No amount of work ever did them harm.
The great triumph of his microscope-making was the
perfection of the stand, known as that of 1876, which elicited
so much favorable comment during our Centennial Exhibition. The invention and practical application of his swinging sub-stage, that enabled him to rotate the illuminating
apparatus completely around the object without disturbing
its focus, were marked examples of his talent. Others may
claim to have made something similar, but none had ever
made it so perfect as to be substantially new to all who used
it. Now no good microscope is made without this important arrangement of the stand. The binocular microscope.
under his hands, became more useful than ever before. It
was not until he had perfected this form that he was willing
to sell a binocular instrument. He knew the good that was
to be obtained by means of the binocular principle, but he
was unwilling to make one for sale until at last he had surmounted all the objections he saw in the system, and had
made so perfect an instrument that he did not fear to
attach his name and reputation to it.
In the construction of his simple form of sliding stage
others may claim the prior invention of the principle in a
crude form, but it is very certain that to Mr. ZENTMAYER,
and to him alone, is due the credit of making this simple
device as perfect as the most costly compound stage, so far
as comfort of working and certainty of motion is concerned.
To suggest is one thing, but to perfect into an efficient
instrument is perhaps the most important after all.
Mr. ZENTMAYER was not willing to push himself forward,
but when he at last was persuaded to lecture on optics at
the FRANKLIN INSTITUTE, his lecture proved to be as well
worthy of the man as all his mechanical work. It stands today as an important addition to the literature of optics.
Mr. ZENTMAYER'S musical education, as well as his artistic,
made him an appreciative critic, and among his countrymen
his poetry is valued. He was so loving and so kind, so winning in his ways, that all who came in contact with him
were attracted towards him, and when his last illness came,
warning them that the mind they had valued so highly
was losing its great strength, they mourned his death long
before the actual dissolution of his body.
After leaving Philadelphia, in 1870, the Chairman of this
Committee saw, of course, less of Mr. ZENTMAYER, although
he had the pleasure of having him stay at his house, in
Hoboken on several occasions, once in company with the
German scientist H. Vogel, and on another occasion with
the eminent investigator and constructor of acoustic instruments Rudolph Koenig; the Chairman, however, always
kept up a correspondence with Mr. ZENTMAYER and sought
his assistance whenever he had need of any instrument
involving especially fine and accurate workmanship.
No words that he could use would be too strong to
express what he knows of Mr. ZENTMAYER personally as a
man of high intellectual acquirements, refined tastes, pure
morality and a sincere amiability which enabled him to
think and speak only kindly even of those who had not
treated him well, and which unspeakably endeared him
to all who enjoyed the privilege of his friendship.
The illness that at last resulted in the death of Mr. ZENTMAYER came on very slowly, and fortunately only after he had
instructed his sons in the processes that had made his work
so celebrated. Those sons have had charge for a number
of years of the construction of the instruments which have
given such great satisfaction to all who have used them.
To members of this Committee the father confided his system of education of his children, and to them he explained
how thoroughly he had informed them of the minutia of his
operations, that they might worthily carry on a business of
which he was so proud. Mr. ZENTMAYER would never do any
work slightingly. What was to be done must be done well,
his constant effort being to improve his methods as well as
improve the construction of his instruments.
His inventions, that have carried the name of ZENT-
MAYER to all parts of the civilized globe, were not made
rapidly, as a rule. He pondered over all his improvements
for a long time, and they all show deep thought. Those
who knew him best remember the look of deep thought
impressed on his speaking face when they called and found
him alone with his big dark-colored work-ing microscope
before him. They knew he was being interrupted in work that
would soon add some new thing to his list of accessories, or
in the perfection of some instrument. With his life has
gone the spirit of a pure-minded and upright man, a good
citizen, a lover of liberty and a lover of truth. To the family
he leaves behind him, if he has not been able to give them
much worldly wealth, he certainly has given a worthy
example for them to follow.
As a writer, Mr. ZENTMAYER was not prolific, preferring
to express his ideas verbally to his friends, rather than to
put them on paper for publication. We find, however, the
following articles, which were his work, in the JOURNAL OF
THE FRANKLIN INSTITUTE:
On a Mechanical Finger for Use in Mounting Diatoms
under the Microscope, 1870, vol. 89, p. 334.
On an Erecting Prism, for Use in the Microscope, 1872,
vol. 93, p. 375. A Lecture on Lenses, 1876, vol. 101, pp. 336
On Improvements in Microscopes, 1877, vol. 104, p. 49.
Also in the Philadelphia Photographer, 1867, vol. 4, p. 251,
we find an article entitled "Refraction without Dispersion,
and some Reflections," in which he takes a hand in the controversy about his photographic lens, with marked ability.
Mr. ZENTMAYER was elected a member of the American
Philosophical Society in 1873, and of the FRANKLIN INSTITUTE in 1865. He received the Elliott Cresson Medal for
improvements in microscopes in 1875.
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