Amici, Giovan Battista
Amici, Giovan Battista
(b. Modena, Italy, 23 March 1786; d. Florence, Italy, 10 April 1868)
optics, microscopy, natural sciences.
Amici was the son of Giuseppe Amici, a ministerial official, and Maria Dalloca, a member of a well-to-do family. In 1806 he married Teresa Tamanini, the daughter of a wealthy Tyrolean bookseller. The following year he graduated as an engineer-architect from the University of Bologna and immediately became a mathematics teacher at the Modena liceo. In 1831 Amici was invited to Florence by the grand duke of Tuscany to head the astronomical observatory and the Royal Museum of Physics and Natural History. He held this office until 1859, when, because of his advanced age of seventy-three, he accepted the less demanding office of director of microscopic research at the museum.
From early youth, Amici was interested in optical instruments, particularly microscopes, and it was in this field that he achieved his fame. In spite of the efforts of many pioneers during the previous two centuries to refine the microscope, in the early nineteenth century scientific microscopy was carried out exclusively with the simple microscope because it performed better than the compound microscope, particularly in resolving power. A comparative study of the microscopes of the past centuries has been made by P. Harting and the Van Citterts, who have thoroughly examined the microscopes in the collection of the Museum of the History of Science at Utrecht. Their study clearly indicates Amici’s decisive contribution to the use of the compound microscope.
In the early nineteenth century, compound microscopes were much less accurate than the simple microscopes, not only because their objectives caused strong aberrations, especially chromatic ones, but above all because the numerical aperture was not yet known to be the determining factor of the resolving power; therefore construction was governed by the erroneous conviction that enlargement was the most important factor. In 1791 the first achromatic lens for compound microscopes was built as the result of the work of an Amsterdam amateur, F. Beeldsnijder; the images were quite good, but the resolution was only 0.01 nmm., while the resolution of simple microscopes reached 0.0015 mm. Only around 1806 did microscopes with achromatic objectives appear on the market, through the efforts of Harmanus Van Deyl, also of Amsterdam; these were instruments that could magnify 150 times and could resolve to 0.005 mm.
This lead was immediately followed by scientists all over the world, especially Chevalier and Nachet; Oberhaüser and Plössl; Tulley, Pritchard, and Ross; and Amici, who was just embarking on his career. Within thirty years, the efforts of these and many other scientists succeeded in making the resolving power of the compound microscope equal to that of the simple microscope. For example, as early as 1818 amici, after having built a type of catadioptric microscope that was free of chromatic aberrations, succeeded in appreciably improving the knowledge of the circulation of protoplasm in Chara cells, thereby becoming immediately famous not only as an optician but also as a microscopic biologist.
His most sensational innovation was achieved in 1837, when Amici arrived at a resolving power of 0.001mm. with a new type of microscope that had a numerical aperture of 0.4 and was capable of magnifying up to 6,000 times. This device consisted of a hemispheric frontal lens applied to the objective; only through this contrivance was it possible to increase the numerical aperture to an appreciable extent. It was the hemispheric lens that permitted maximum use of the compound microscope. All opticians, with the exception of the French, immediately adopted this new design.
The improvement introduced by Amici also led to a significant theoretical clarification. The moderate influence of the magnification in the operation of the microscope was soon recognized and values ranging around 1,000X were generally achieved. It was emphasized, however, that resolution was due mainly to the numerical aperture and to the optical correction by the objective. Amici clearly stated his discovery in a letter of 25 October 1855 to his friend Ottaviano Mossotti, professor at the University of Pisa and a famous optical mathematician; the following passage is particularly interesting:
The objectives of my microscopes consisting of six lenses, three crown lenses and three flint lenses, happen to be achromatic. I found out, however, that the sets consisting of three pairs of lenses, as I mentioned, were not the best suitable for achieving greater magnification, particularly due to the fact that the lower pair closer to the object are too large and make it impossible to obtain a very short focal distance of the system and its very large aperture. I then had the idea of replacing the lower pair with a simple lens, i.e., a half-sphere of any transparent substance, either crown, flint, low-grade ruby, diamond, molten rock crystal, etc., and thus eliminating its aberrations by means of the two suitably processed upper pairs. In order to accomplish this, I needed a flint with very high dispersion, which I was able to obtain from Faraday thanks to Airy. The English opticians laughed at this request but, when I showed them the superiority of the new construction in London in 1844, they soon tried to imitate it, and the Americans followed suit. The French, who were not interested and who were unable to understand the improvement, were outdistanced by the others.
Amici was so convinced that the numerical aperture was the theoretical factor determining a microscope’s power that he continued to do everything possible to increase it, not only by manufacturing objectives with ever greater numerical aperture (Harting states that in 1856 he purchased from Amici a microscope objective with a numerical aperture of 0.985) but also by inventing the technique of immersion microscopy; he first used water, then olive oil, and finally sassafras oil. He even became aware of the influence that the thickness of the cover glass has on the quality of the image in the microscope.
Amici moved to Florence, where he devoted his attention to other optical processes, although his interest in microscopy never flagged. He invented widely used prisms that still bear his name, and reconsidered the direct-vision prism, which had been forgotten. He also built concave mirrors and astronomical lenses. His masterpiece was a lens with a diameter of 285 mm.: this was so far in advance of his time that it was presented as a rarity to the Third Congress of Italian Scientists, held in Florence in 1841. Only one lens larger than this existed at that time. Amici’s lens was so successful that it is still in use at the Arcetri Astronomical Observatory. Amici also invented new micrometers to improve the accuracy of astronomical measurements, and new types of distance–measuring telescopes.
While Amici kept increasing the power of his instruments, through his theoretical know-how and his skill in optical processing, he also used them in astronomical and microscopical; observations. His findings in microscopy attracted the attention of the entire biological world of his time. Besides studying the circulation of protoplasm, Amici made remarkable observations in anatomy, physiology, histology, and plant pathology, as well as in leaf morphology (discovering palisade parenchyma) and animal biology. The discovery that made him famous, however, was that of the fertilization of phanerogams, particularly the travel of the pollen tube through the pistil of the flower (1821). His early observations were followed by a heated controversy with the best–known botanists of the world, who for thirty years disputed Amici’s ideas. However, by making ever finer microscopic observations, he finally won over his rivals.
The splendid wax models by which Amici illustrated the results of his microscopic observations can still be seen in many museums of natural history.
I. Original Works. Amici’s main works in optics and astronomy are “Descrizione di un nuovo micrometro,” in Memorie di matematica e fisica della Società Italiana delle Scienze, 17 (1816), 344–349; “Dei microscopii catadiottrici,” ibid., 18, no. I (1818), 107–118; “Memoria sopra un cannocchiale iconantidiptico,” in Memorie della Società Italiana delle Scienze, 1 (1821), 113–125; Description d’une nouvelle lunette micrométrique (Genoa, 1823), IX, 517–521; Osservazioni sopra i satelliti di Giove (Genoa, 1823), IX, 517–521; Osservazioni sopra i satelliti di Giove (Genoa, 1825), XII, 539–560; “Descrizione di un nuovo strumento per livellare,” in Atti della R.e.I. Accademia dei Georgofili, 15 (1837), 129–137; “Lettura relativa a due macchine ottiche da lui inventate,” in Atti della Prima Riunione degli Scienziati Italiani (Pisa, 1839), pp. 49–50; and “Di alcuni perfezionamenti recentemente ottenuti in fotografia,” in Atti della Sesta Riunione degli Scienziati Italiani (Milan, 1844), pp.87–97.
Amici’s principal publications in biology are “Osservazionoi sulla circolazione del succhio nella Chara,” in Memorie della Società Italiana delle Scienze, 18 (1818), 183–198; “Osservazioni microscopiche sopra varie piante,” ibid., 19 (1823), 234–255; “Descrizione di alcune specie nuove di Chara,” in Memorie della R. Accademia di Scienze, Lettere ed Arti di Modena, 1 (1833), 199–207; “Opinione relativa all’ascensione della linfa nelle piante,” in Atti della Prima Riunione degli Scienziati Italiani (Pisa, 1839), pp.165–167; “Sulla presenza dei pori nei casi delle conifere e sulla loro struttura,” ibid., pp. 162–164; “Sul processo col quale gli ovuli vegetabili ricivono l’azione fecondante del polline,” ibid., pp. 134–139; “Sull’uredo rosae,” ibid., p. 157; “Sulla fecondazione delle piante (cucurbita pepo),” in Atti della Quarta Riunione degli Scienziati Italiani (padua, 1842), pp. 134–139; “Nuove osservazioni sugli stomi del Cereus Peruvianus,” ibid., pp. 327–333; “Sulla struttura degli stomi,” in Atti della Sesta Riunione degli Scienziati Italiani (Milan, 1844), pp. 513–518; “Sulla fecondazione delle orchidee,” in Atti della Ottava Riunione degli Scienziati Italiani (Genoa, 1846), pp. 542–550; “Nota in risposta al primo articolo dello Schleiden,” ibid., pp. 89–90; “Sulla malattia dell’uva,” in Atti della I.e.R. Accademia dei Georgofili, 30 (1852), 454–460; “Sulla malattia della foglia del gelso, detta fersa o seccume,” ibid., n.s. 1 (1853), 72–79; “Sulla malattia del frumento detta rachitide,” ibid., 570–577; and “Sulla fibra muscolare,” in II tempo, 1 (1858), 2–4.
Amici’s correspondence, which consists of more than 6,000 letters and has not yet been published, is in the Biblioteca Estense of Modena.
II. Secondary Literature. The principal publications on Amici are Celebrazione del centenario della morte di G.B. Amici (Modena, 1963); G.B. Donati, “Elogio del Prof. G.B. Amici,” in Reale Accademia dei Georgofili, 1 (1864), 1–23; H. von Mohl, “Giovambattista Amici,” in Botanische Zeitung, 15 (1863), 21–32; P. Pagini, “L’ottica geometrica in Italia nella prima metà del secolo XIX e l’opera di G.B. Amici,” in Rassegnanazionale (1917), 1–35; F. Palermo “Sulla vita e le opere di G. B. Amici,” in Bollettino di bibliografia e storia delle scienze matematiche e fisiche, 28 (1870), 3–18; V. Ronchi, “sopra gli obbiettivi astronomici dell’Amici,” in Rivista d’ottica e meccanica di precisione, 2 (1922), 3–21; and “Giovan Battista Amici, Optician,” in Atti della Fondazione Giorgio Ronchi, 18 (1963), 481–504; and P.H. Van Cittert and J. G. Van Cittert-Eymers, “The Amici Microscopes About 1850 in Possession of the University of Utrecht,” in Proceedings of the Koninklijke Nederlandsche Akademie van Wetenschappen, 50 (1947), 5–10.
Also of value for an understanding of the microscope and its development are P. Harting, Das Mikroskop, 2nd German ed. (Brunswick, 1866); Maria Roseboom, Microscopium (Leiden, 1956); and P. H. Van Cittert and J. G. Van Cittert-Eymers, “Some Remarks on the Development of the Compound Microscope in the 19th Century,” in Proceedings of the Koninklijke Nederlandsche Akademie van Wetenschapen, 54 (1951), 1.