The Ploessl ocular (“eyepiece”) is easily the most popular design in the hobby. Regardless of focal length, from 40 mm to 4 mm, they are common because they are inexpensive and they reasonably support the limits of the largest amateur instruments. Better designs are available, but at a greater cost. Thus, the Ploessl is the first choice, whether for a refractor, reflector, or catadioptric telescope. For all of its ubiquity, its inventor, Viennese optician Simon Georg Ploessl is not widely known among astronomers.
First of all, he spelled his name Plößl and that almost rhymes with the English word “vessel.” The character that looks like a capital-B ß is a double-s. The umlaut-o ö is sounded by rounding your lips to say English long-o, but instead, saying English long-a. If you did not grow up speaking German, then “Plessl” is close enough. That is because three consonants follow the vowel. Each one clips some time off the sounding. The word for “height” die Höhe sounds like an American calling their friend from across a room “hey-yeh” not the short laugh “heh.” For the signature on his nameplates, Ploessl also used the ligature œ (oe), a less common flourish. He also used both versions of his given name: Georg Simon and Simon Georg. If your typewriter has no umlaut vowels (ä ö ü) or a sharp-s (ß), you can use an e and a double-s. Thus, Plößl (which is how he spelled it) is accepted as Plössl or Ploessl, but spelling the name Plossl or saying it that way is wrong.
Georg Simon Plößl (1794-1868) was born in Wieden, which had been an independent villa in the Middle Ages but by the 18th century already lay within Vienna’s shadow. He was the son of a cabinetmaker. And therefore an apprentice in his father’s shop. When he was 18, he left for the optical firm Voigtländer, starting on May 9, 1812. In 1823, he moved back to his father’s home and began his own laboratory and workshop for investigations into the production of optical instruments. In 1828 he was open for sales. At first, Ploessl made microscopes, and he soon became famous for them. His company took a new direction when he sold a microscope to Joseph Franz von Jacquin, professor of botany and chemistry at the University of Vienna. Von Jaquin introduced Ploessl to the astronomer Joseph Johann von Littrow for whom he built a telescope in 1830.
By 1850, in addition to the microscopes which were the primary production of his firm Ploessl had delivered refractors to observatories in Romania, Hungary, Greece, and Russia. In 1851 the firm delivered an 11-inch
Three factors kept this system from becoming widely accepted. First, telescopes are durable goods. Better ones have been built since 1610, but the old ones still work. The Ploessl refractor in Athens served the university until 1940. Second, astronomy was a private pursuit for intellectuals of independent means. While Britain had its Royal Astronomer, few such public posts existed elsewhere. Ploessl built telescopes for state enterprises in Greece and Russia, but he built more for wealthy patrons in Hungary, Romania, and Italy. Only with the explosion of science in the 20th century was there any broad consumer demand for the instruments of empirical discovery. Third, as prosperous as the Ploessl firm was, it was a sole proprietorship. When Simon Ploessl was killed by a falling sheet of glass in 1868, there was no one to step into leadership. The firm continued until 1905, but there was no visionary to drive the effort.
For example, consider Pleasures of the Telescope (1901) by Garrett P. Serviss. Serviss was famous as a popularizer of science, especially astronomy. When he was a night editor at The Sun of New York, one of his lecture tours was subsidized by Andrew Carnegie. His passing was noted in a long obituary in Popular Astronomy (August-September 1929). The Pleasures of the Telescope was first published by Putnam in 1901, and then went through several re-publications. Google Books and Hathi Trust provide the 1915 printing by D. Appleton and Company. Serviss described two kinds of eyepieces: positive (Ramsden) and negative (Huygens). He does not mention the Ploessl.
Further Reading
The Hellenic Archives of Scientific Instruments at http://www.hasi.gr/makers/ploessl-georg-simon
https://de.wikipedia.org/wiki/Simon_Plößl
Looking at the Skies for 175 Years: The 162-mm Ploessl Refractor and the 400-mm Gautier Refractor of National Observatory of Athens, Panagiotis, Lazos and Tsimpidas, Dimitrios; XXXVII Scientific Instrument Symposium, 3-7 September 2018, Leiden and Haarlem.
https://en.wikipedia-on-ipfs.org/wiki/Bicske.html
“Plössl-Mikroskope - ein Vergleich mit modernen Geräten,” by E. Steiner and P. Schulz, ©Naturhistorisches Museum Wien, download from www.biologiezentrum.at
“The Achromatic Telescope, Dialytes, and Fluid Lenses--Nebula--Double Stars—Occultations” by the Rev. T. W. Webb, A.M., F.R. A. S., The Intellectual Observer, Groombrdige and Sons, London, No. XLIX, February 1866.