Emile Bertrand, 1844 - 1909

by Brian Stevenson
last updated March, 2024

Emile Bertrand was a graduate of School of Mines of Paris, and worked primarly as a mineralogist. From about 1872 through 1885 he operated “Comptoir Minéralogique, Géologique et Paléontologique”, a shop that specialized in geological specimens and supplies.

Bertrand developed many new forms of apparatus to facilitate his mineralogical studies. One of his best known inventions is the “Bertrand lens”. This is an additional lens in a petrological microscope, located in the body tube between the objective and ocular lenses, whose height can be adjusted. The Journal of the Royal Microscopical Society reported in 1883, “Above the objective … is inserted a slide … with an achromatic lens so as to use either parallel or convergent light as may be desired, the slide being raised or lowered by a rack-and-pinion movement”.

However, Emile Bertrand was not a professional microscope maker. To the best of my knowledge, only two microscopes are definitely known to have been built/modified to his specifications, and those were for his personal use (Figures 1 and 2). A third microscope that strongly resembles Bertrand’s design may have been built or modified to his orders (Figure 3). Bertrand wrote of using lenses that were manufactured by Nachet, and many of his other microscope components likely came from commercial suppliers.

Eugène Trutat described one of Bertrand’s personal microscopes in his 1883 Traité Élémentaire du Microscope (1883), and lamented that the were not available for purchase by the public: “le microscope n'est pas absolument dans le commerce, mais il est possible d'obtenir de ce constructeur quelques instruments de commande” (“the microscope is absolutely not available commercially, but it is possible to obtain some control components from this manufacturer”), and “il est à regretter que cet excellent instrument ne soit pas dans le commerce d'une manière complète; mais, comme nous l'avons déjà indiqué en note, il est possible d'obtenir quelques instruments de M. Bertrand” (“it is to be regretted that this excellent instrument is not on the market in a complete form; but, as we have already indicated in a note, it is possible to obtain some components from Mr. Bertrand”).

It can be stated with certainty that Emile Bertrand was neither the inventor nor manufacturer of a type of small drum compound microscope that mounts on its wooden case, commonly known as the furnace microscope (Figure 4). The authors of The Billings Microscope Collection inexplicably attributed such instruments to a Parisian manufacturer named “Bertrand”, and gave a production date of 1839. They did not provide any evidence for that attribution. If they intended to attribute Emile Bertrand to these microscopes, a possible explanation is that Bertrand sold such instruments in his geology shop, and that the authors were aware of an example that bears Bertrand’s sales label. Supporting that idea, numerous examples are known that bear names of sellers in France and England, and they were advertised for sale in the USA during the mid-1870s. The alleged date of 1839 is probably too early, as these instruments do not resemble French drum microscopes of the 1830s or 1840s. Joseph Molteni, who was a major manufacturer of microscopes and other scientific devices, advertised that he made this type of microscope in 1859 (Figure 4).

Figure 1. A ca. 1883 petrological microscope that was once owned by Emile Bertrand and was built to his specifications. The “Bertrand lens” and its adjusting wheel are visible on the body tube, immediately above the objective lens. Left, engraving from Eugène Trutat’s “Traité Élémentaire du Microscope (1883). Center and right, adapted from “Collectible Minerals” and Jacques Touret “Le Microscope Polarisant à l’Assaut des Montagnes“, for educational, nonprofit purposes. “The Journal of the Royal Microscopical Society” described this instrument in 1883: Above the objective at F is inserted a slide L with an achromatic lens so as to use either parallel or convergent light as may be desired, the slide being raised or lowered by a rack-and-pinion movement, the milled head of which is shown at P. A slow motion is given to the rotating plate of the stage by a tangent screw terminating in the milled head T. This screw works in a clamp which can be screwed to the stage, and when tightened up the rotation of T causes the clamp, and with it the stage, to revolve. When the clamp is loosened the stage can be revolved by the hand. This mechanism effecting the slow rotatory motion of the stage is similar to that generally applied in the construction of theodolites and alt-azimuth instruments. The body-tube is graduated and the focal distance is read by means of a vernier on the limb; the milled head of the fine adjustment r is divided; the rectangular movements of the mechanical stage are also each provided with a scale and vernier, while the margin of the stage is graduated and has two fixed verniers. At F can be inserted a mica quartz-plate or a quartz prism. There is a spring clip for rapidly attaching the objectives".


Figure 2. Described as “The first model of polarizing microscope built by Emile Bertrand, while he was still a student at the School of Mines” (late 1860s). Adapted from Eugène Trutat’s “Traité Élémentaire du Microscope (1883), and for educational, nonprofit purposes from Jacques Touret “Le Microscope Polarisant à l’Assaut des Montagnes”.


Figure 3. An unsigned petrological microscope that strongly resembles Bertrand’s ca. 1860s first model (see Figure 2). It may have been built/modified under Bertrand’s supervision. Adapted for nonprofit, educational purposes from an internet auction site.


Figure 4. “Furnace” microscopes. (Left) Excerpt from “The Billings Microscope Collection”, attributing this microscope to “Bertrand”. As discussed above, the authors of that catalogue did not give a reason for their attribution. We suggest that it is possible that they were aware of an example with Emile Bertrand’s trade label attached, as it is likely that he sold various scientific instruments in his geological shop. Several other examples are known with various other retailers’ names attached. (Center) An unsigned example. (Right) Excerpt from Joseph Molteni’s 1859 catalogue. Molteni was a major manufacturer of microscopes, and may well have been the producer of the Billings’ “Bertrand” microscope.


Figure 5. Emile Bertrand, from the obituary that appeared in “Bulletin de la Société Française de Minéralogie”.


Emile Bertrand was born in Paris on February 5, 1844, the first son of Jean Barthélemy Bertrand and Marie Eugénié Héron. Father Jean was a judge in the Paris Court of Cassation, and a Chevalier of the Légion d'Honneur.

Emile attended the School of Mines of Paris, graduating in 1869. The 1870 Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration listed his occupation as “ingénieur civil”, located on Rue de Gay-Lussac. He published his first scientific paper that year, “Notice sur le tellure natif du Chili”.

Bertrand opened “Comptoir Minéralogique, Géologique et Paléontologique” at 15 Rue de Tournon ca. 1872.

He married Marie Juliette Naudot on April 26, 1873.

Bertrand was one of the founders of the Société Française de Minéralogie et de Cristallographie, in 1878. He twice served as its president.

In 1879, Bertrand sold all of the paleontological specimens from his shop to Ward’s Natural Science, of New York (Figure 6). Bertrand’s shop was henceforth known as “Comptoir Minéralogique et Géologique”.

As noted above, Bertrand had worked since his days as a student on techniques to improve the study of mineral characteristics. These included development of the “Bertrand lens” and other additions for the petrological microscope. In 1883, Eugène Trutat lauded Bertrand’s inventions in his Traité Élémentaire du Microscope, while expressing regret that Bertrand did not reproduce his personal microscopes for the commercial market (although Nachet and other manufacturers did adopt Bertrand’s technologies for their products). Also in 1883, The Journal of the Royal Microscopical Society reproduced images from Trutat’s book, along with the description reproduced above in the Figure 1 legend, and this description of Bertrand’s stage-mounted goniometer:

A special form of goniometer is adapted to the stage, for measuring the distance apart of the optic axes in air or in oil or other liquids. The object is held in forceps attached to a spindle connected with the smaller of the two milled heads. This rotates independently for adjusting the object or can be withdrawn if required. When the adjustment has been made the rotation of the larger milled head, to which a vernier index is attached, carries with it the inner spindle and forceps, and the extent of the inclination thus given to the object is measured by the index on the graduated semicircle G. The circular box C holds the liquid, and has an aperture at the bottom closed with a glass plate admitting light from the mirror.” (Figure 8).


In 1883, a mineralogist colleague, Augustin Alexis Damour (1808-1902), named a newly discovered mineral “Bertrandite”, in honor of Emile Bertrand.

Bertrand sold his mineral shop to a Dr. Emmanuel Dagincourt in 1885. It appears that Bertrand worked for the rest of his career with the Ministry of Mines. He moved to 62 Boulevard St. Michel in 1885, then to 2 Rue de la Planche in 1886.

Emile Bertrand died on November 16, 1909, after a long illness, at the age of 65. His obituary in Bulletin de la Société Française de Minéralogie read:

On November 16, one of the last survivors of the founders of our Society died, having been its president twice and who, in his all too-short career, rendered invaluable services to Mineralogy.

The period of his scientific activity was short, in fact. Born in 1844 to a very wealthy family, he left the École des Mines in 1869 as a civil engineer with a real passion for Mineralogy. After two or three years of travel in France and abroad, in 1872 he began a series of researches, first very spaced out, then succeeding one another at short intervals until around 1890. After that date, there was only a Note in 1896 and his last work in 1897. This sudden cessation of productivity that had initially given such brilliant results was caused by an illness that worsened over the years, resulting in almost complete amnesia and a series of congestions, the last of which lasted for 48 hours.

Bertrand's work can be divided into two distinct parts: description of a large number of new or rare and poorly known minerals, and invention of new observation methods. In these two areas of research, which require very different skills, he exhibited first-rate abilities. He was an observer of rare sagacity, and he possessed, it can be said, a true genius for the apparatus.

Those who have not worked with old instruments can hardly realize the revolution that occurred when the instruments imagined by Bertrand appeared. It was the discovery of a new, unsuspected world in which we found, from the very first steps, facts of capital importance.

The Amici microscope and the Nörremberg apparatus, which old mineralogists keep in a corner of their cabinet like venerable relics, had undoubtedly given, in the skillful hands of Grailich, Lang, and especially Des Cloizeaux, very interesting results, but their application was singularly limited and we quickly reached their limit. They required the use of large plates, and therefore needed large crystals which are always rare, even among artificial substances whose conditions of formation can readily be modified. In the vast majority of cases, it was impossible to determine the symmetry of crystals and their optical constants, either because they were too small or because it was not possible to cut them. Observation in parallel or convergent light at high magnifications had therefore been a scientific problem for a long time and, on all sides, physicists and device manufacturers sought in vain to resolve it. E. Bertrand solved it with an artifice as simple as it was elegant, and he solved it so completely that since then we have only needed to improve the details of construction without touching the principle. The lens inserted between the objective and the eyepiece, and which is the characteristic of the device, will always bear the name of Bertrand lens, just as the polarizing prism has for a century borne the name of Nicol prism.

It is fair to say that at the same time, in 1877, another solution to the same problem appeared. Mr. von Lassaulx had shown that it was possible to transform an ordinary microscope into a converging light device, without any additional lens, but the images thus obtained, very clear it is true, were too small to lend themselves to somewhat exact measurements. This was also a very simple and elegant process, but only suited to purely qualitative observations in some cases and could not compete with Bertrand's instrument which was, from its appearance, universally adopted by mineralogists and crystallographers from all countries.

E. Bertrand did not stop at this first success. Constantly concerned with broadening the field of application of his microscope, to make it in some way a universal instrument suitable for all qualitative and quantitative observations on crystals that escape macroscopic methods, he imagined a micrometer eyepiece allowing approximate measurementof the spacing of optical axes, and which served as the first idea for the much more precise device proposed by Mallard a few years later. For a long time we recognized the great difficulty of measuring extinctions in parallel light, the eye having difficulty appreciating the moment of maximum intensity of the shadow. He imagined the four-quartz eyepiece, with which we no longer have to distinguish between light and dark, but between two very different hues, and which allows infinitely greater precision in measurements. Finally, a very ingenious device that permits measurement of the dihedral angles of crystals not exceeding 0.1 mm, if not in a very exact way, at least with a sufficient approximation to calculate the geometric constants.

The improvements made by E. Bertrand to the methods of observing the optical properties of crystals are not limited to the construction of his microscope. The great fault of devices of this type is the smallness of the field of vision, because a large nicol is much too long to be placed between the illuminating mirror and the plate. To obviate this serious drawback, E. Bertrand constructed polarizing prisms which, with half the length, gave an almost double field. If we add to this series of improvements the wide aperture angle objective which made it possible to see the optical axes whose spacing exceeded 130°, we will see that Bertrand's microscope made enormous progress over the old instruments, and we will understand the considerable influence he exerted on the rapid advancement of crystal physics. We can affirm that without him Mallard would not have been able to bring to fruition his beautiful theory of crossing thin blades and the structure of pseudo-symmetric bodies.

The list of devices that we owe to E. Bertrand is not yet exhausted. He imagined a refractometer of extremely simple construction which nevertheless allowed an approximation of one or two units of the third decimal in the index measurement. He did better: he built a pocket refractometer which, despite its small dimensions, provided in many cases a rapid means of recognizing minerals without resorting to any other physical or chemical test.

In possession of these new means of study, E. Bertrand undertook the revision of a large number of minerals whose exact determination could not be made with old instruments. The list of mineral substances whose difinition he corrected was long, but he dreamed of reviewing everything that was doubtful, and he would certainly have accomplished this considerable work, if illness had not suddenly stopped his career.

With his ardor at work, with his incomparable skill, with this particular flair that the sciences of observation require and which he possessed to a high degree, he could certainly do much more than he did, but his work, as it is, ensures his name an eminent place in the history of Mineralogy.

Figure 6. 1879 notice from “The American Journal of Science”, announcing that Emile Bertrand had sold all of his fossil specimens to Ward’s Natural Science. His business was thereafter known as “Comptoir Minéralogique et Géologique”.


Figure 7. Examples of minerals from Emile Bertrand’s collection. Adapted for Center and right, adapted for educational, nonprofit purposes from “Minéraux: Objets de Collection”.


Figure 8. Bertrand’s 1883 stage-mounted goniometer. See text above for details.


Figure 9. An example of a Bertrand refractometer. Adapted with permission from http://www.lecompendium.com/dossier_optique_63_refractometre_de_poche_bertrand/refractometre_bertrand.htm



Thank you to Albert Balasse for permission to reproduce images of his Bertrand refractometer.



American Journal of Science (1879) Advertisement from Emile Bertrand, advertiser section, page 4

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1870) “Bertrand (Emile), ingénieur civil, Gay-Lussac”, page 135

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1874) “Bertrand (Emile), ingénieur civil des mines, Tournon 15”, page 135

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1884) “Bertrand (Emile), ingénieur civil des mines, Tournon 15”, page 160

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1885) “Bertrand, ingénieur des mines, boul. St. Michel, 62”, page 161

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1886) “Bertrand, ingénieur des mines, boul. St. Michel, 62”, page 178

Annuaire et Almanach du Commerce, de l'Industrie, de la Magistrature et de l'Administration (1886) “Annuaire géologique universel, directeur: docteur Dagincourt, rue de Tournon, 15”, page 788

Annuaire Géologique Universel et Guide de Géologue (1886) “Bertrand Em., Ingénieur des mines, rue de la Planche 2, Paris. Min. cryst. optiq. coll. min.”, page 73

Bertrand, Emile (1870) Notice sur le tellure natif du Chili, Neues Jahrbuch für Mineralogie Geologie und Palaeontologie, page 465

Bulletin de la Société Française de Minéralogie (1910) Emile Bertrand, pages 116-124

Bulletin de la Société Géologique de France (1883) Members “1869 Bertrand (Émile), rue de Tournon, 15, à Paris

Collectible Minerals (2023) On the exhibition of September 6, 2023 - March 9, 2024, Musée de Minéralogie Mines Paris, https://www.musee.minesparis.psl.eu/Donnees/data16/1629-livret_expo_mineraux_musee_mines_EN_LD.pdf

Damour, A. (1883) Note et analyse sur le nouveau minéral des environs de Nantes, Bulletin de Minéralogie Année, pages 252-254

Death record of Emile Bertrand (1909) accessed through ancestry.com

Friedel, Georges (1893) Cours de Minéralogie, G. Masson, Paris, pages 281-282

Jannettaz, Édouard (1910) Les Roches et Leurs Éléments Minéralogiques, Fourth edition, A. Hermann et Fils, Paris, pages 147-149

Journal of the Royal Microscopical Society (1883) Bertrand’s petrological microscope, pages 413-415

“J.W.J.” (1914) Evolution of the petrological microscope, Nature, pages 314-315

Marriage record of Emile Bertrand and Marie Juliet Naudot (1873) accessed through ancestry.com

Mineralogical Magazine (1910) Emile Bertrand (1844-1909) page 442

Neues Jahrbuch für Mineralogie Geologie und Palaeontologie (1872) “Das ‘Comptoir Minéralogique, Géologique et Paléontologique von Emile Bertrand in Paris’ befindet sich jetzt: Rue de Tournon Nr. 15”, page 112

Paris voter registration of Emile Bertrand (1891) Address: la Planche 2, accessed through ancestry.com

Touret, Jacques (2012) Le Microscope Polarisant à l’Assaut des Montagnes, Travaux du Comité Français d’Histoire de la Géologie, pages 67-80, https://hal.science/hal-01065569/document

Trutat, Eugène (1883) Traité Élémentaire du Microscope, Gauthier-Villars, Paris, pages 266-270