"Mr. Justice described a superior microscope stand made by Mr. Zentmayer, of Philadelphia, for and under the direction of Dr. Hunt, of Philadelphia, and embracing all of the important late improvements. Dr. LeConte added testimony to the admirable skill of the mechanician, and supported it by referring to the stand lately made by him for Dr. Goddard, and to the stand now making for the Academy of Natural Science, which promises to be one of the best extant."
Zentmayer called this first stand the "Grand American".While this massive instrument was beautifully constructed, it lacked any truly novel improvements over the best English stands of the time, except for the optional revolving stage with sliding glass plate slide holder. As measuring the angular aperture of objectives had already become the rage at that time, the Grand American was made to rotate on its base, which allowed angular measurements on a silvered degree scale with the microscope tilted in the horizontal position. The Grand American was produced from 1858 to 1876, although probably in quite low numbers, since the cost of the fully equipped stand was over $700, the most expensive of any of the top of the line American microscopes. Most of the exquisite accessories to this stand, shown on p11 are identical to items in the catalog of Beck or other English makers. However, the optional sliding glass plate on goniometer stage is a unique contribution by Zentmayer. The slide holder was pressed againts two rails on the stage by an ivory tipped screw. This design works extremely well and was used for decades and also incorporated into smaller instruments, such as the American Histological stand. The following remarks in the American Naturalist of 1873 address the origin of this device:
"The glass sliding stage, moving upon a circular plate having concentric and graduated rotation, has become, and still is becoming, so important a contrivance in microscopy that its origin is a question of some importance. This stage seems to be known in Europe as Nachet's invention, and it was, doubtless, from his new style of Student's Microscope that it was adopted by London makers. Mr. Joseph Zentmayer of Philadelphia, who had made the plain glass stage long before that time, constructed in the spring of 1859, for a Mr. Rosevelt of New York, a revolving glass stage which would be minutely and quite accurately represented by Dr. Carpenter's description (The Microscope, London, 1868, pp68-69). He continued to make these stages, and in the year 1864 furnished one to Prof. Edwin Emerson, then in Paris, who took pains to show the American stand to those interested in microscopes and especially to the makers. In October of the same year, Mr. (now Dr.) W.W. Keen of Philadelphia exhibited one of these stands, wih a similar stage, to Nachet, and the following spring placed it in his hands for safe packing for return to this country. These goniometer stages were certainly substantially the same as those now made, and were probably equal to any of the latter in delicacy of adjustment and finish; and it would seem that the publicity then given them should guarantee to their maker the credit for their invention."
In 1862, Zentmayer began building the U.S. Army Hospital microscope to meet the needs of the Civil War. This model was produced for over 30 years, undergoing many gradual modifications, until finally it had incorporated the swinging substage and redesigned limb and long lever fine focus patented by Zentmayer, and eventually even a horseshoe foot. Unlike the larger stand, the Army Hospital stand is commonly encountered today and must have been made in fairly large numbers. The cost of the basic Army Hospital stand in 1879 was $90, with the fully equipped binocular version going for $173.
In 1866, Zentmayer received a patent for a photographic lens that used various pairs of meniscus lenses interchangeably to produce various focal lengths. The patent caused a great deal of controversy, with Zentmayer first having to prove priority over a similar patent by Steinheil, while, at the same time suffering ridicule by a photographic journal that claimed the lens was an "impossibility or valueless device". Finally, when the lens did prove its worth in the field, C. B. Boyle, of New York, wrote to the Philadelphia Photographer, also claiming priority of invention, and apparently even altering patent drawings to make his resemble Zentmayer's lens. The debate and controversy was reported in issues of Humphrey's Journal, The Journal of the Franklin Institute, and The Philadelphia Photographer.
According to Coleman Sellers, writing in the Journal of the Franklin Institute, in 1888, "Mr. Zentmayer's office in Walnut Street, where he had his lathe close to his counter and near to the cases containing 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". Zentmayer participated in the "Philadelphia Photographic Expedition" to observe and photograph the solar eclipse of August 7, 1869, not only by building the photographic lenses and shutters for the telescopes, but, also traveling to Ottumwa, Iowa, to take part in the observations. Luckily, he was present at the Ottumwa site, since the clockwork for the Gettysburg College telescope to be used there had been damaged in transit and he was the only member of the three parties stationed across the Iowa path of the eclipse that was capable of repairing the instrument.
In 1869, Zentmayer made an interesting adjustable diaphragm, using a pair of rollers with a conical groove in their centers, which, when rotated in unision, causes the circular opening between them to change size. This invention was reported in the 1869 Journal of the Franklin Institute. In 1870, the American Journal of Science reported on a new mechanical finger invented by Zentmayer, which mounted on the microscope stage and allowed the operator to manipulate diatoms and other small objects. In the same year, Zentmayer wrote an article describing this device for the Journal of the Franklin Institute. Writing articles and even letters to the journals was something Zentmayer rarely did, considering his importance as an instrument maker and his excellent relationship with much of the scientific community.
In 1872, both the American Naturalist and the Journal of the Franklin Institute reported on Zentmayer's new erecting prism for the microscope. The single prism was placed just above the objective.
1876, the centennial of the American Revolution, was a pivotal year in American microscopy. Zentmayer was granted an important patent that year, upon which he based much of his new line of instruments. U.S. Patent #181120 covered the swinging substage assembly and mirror as well as the redesigned fine focus, consisting of a long lever mounted in the limb. These inventions were incorporated into the new version of his top of the line instrument - now called the American Centennial. The reign of the Grand American had ended. He also introduced a small instrument with unique hollow conical pillar, called the American Histological microscope. These new instruments debuted at the 1876 Philadelphia International Exhibition.
The well-known London microscope maker, Henry Crouch spent the summer of 1876 in Philadelphia, exhibiting his stands at the Centennial exhibition and visiting with the American makers. He spent some time with Zentmayer and mentioned him most favorably in an article in the American Naturalist in 1877. He especially praised Zentmayer's new portable microscope, apparently referring to the rare box-mounted folding microscope (see SMMA #31). Of American stands, he judged Zentmayer's to have no superiors anywhere.
A new student microscope based on the American Histological stand, but with fewer refinements, was also introduced in 1876 and reported in the American Naturalist in 1877. By 1878, a heated debate was raging in the pages of the American Journal of Microscopy as to who deserved credit for the swinging substage. The main combatants were Bulloch, of Chicago, and Zentmayer. Gundlach also held an 1876 patent for a swinging mirror, while working for Bausch & Lomb. Their first stands sent to Philadelphia did not have the substage swinging in the axis of the object, however, later in the summer they sent stands that did include this feature. Previously, both Bulloch and Crouch, of London, had claimed priority for the concentric rotating stage. However, Zentmayer's stage was shown to have originated many years earlier, in the Grand American.
Zentmayer began the manufacture of Prof. Ryder's automatic microtome in 1887. An article on this device appeared in the American Monthly Microscopical Journal, 1887. Joseph Zentmayer died in 1888, after a prolonged illness. The business was continued by his sons during the early 1890's. An article in the American Monthly Microscopical Journal, in 1892, describes the American Continental stand, introduced by Frank Zentmayer, with a horseshoe base.
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