John Tyndall

1820 (Leighlinbridge, Ireland) – 1893 (Hindhead, England)

Tyndall has been described as “the greatest experimental physicist of the Victorian age” for his wide-ranging work, and was the first to prove the greenhouse effect. Frankland and he met as young teachers, and studied together under Bunsen in Marburg. He collaborated with Knoblauch (one among his huge range of correspondents, many German) and researched in Magnus’s Berlin laboratory. A member of Huxley’s ‘X-Club’, he was greatly admired by his friend Faraday, translated Helmholtz, defended Pasteur, and tangled with Joule. A great climber and hiker, he visited Muir at Yosemite, and wrote to his friend Darwin about mucus and nostril-hair.

Joseph Black

1728 (Bordeaux) – 1799 (Edinburgh)

Black, known for his discovery of latent heat, specific heat and carbon dioxide, was an influential member of the Scottish enlightenment. Cullen (who had taught him) and Watt (a close collaborator) became lifelong friends — in Watt’s case, after their Glasgow days, mainly by correspondence. Smith (another friend for life), Hutton, Hume and Ferguson were among his clubbable Edinburgh circle; he was Hume’s doctor, and sold a house to Ferguson. With Smellie and his close friend Hutton, he was a regular at Monboddo’s weekly ‘learned dinners’. He entertained Franklin, taught Beddoes, and was present when Burns met Scott.

Jean-Antoine Nollet

Abbé Nollet

1700 (Pimpré, France) – 1770 (Paris)

Nollet was a serious experimenter, a scientific showman, and purveyor of scientific instruments to the wealthy, Voltaire included. He assisted du Fay and Réaumur at the Académie des Sciences. Franklin (with whom he disagreed), Spallanzani (with curiously-overlapping interests) and Volta were correspondents. In Leyden, Nollet visited Desaguiliers, s’Gravesande and Musschenbroek (who invented the Leyden jar — named by Nollet — and showed him a way of making moving images). Lavoisier, Monge and Coulomb were among his students. After visiting, he corresponded for 2 decades with Bassi, Europe’s first female professor.

Jean-Antoine Nollet knew…

Henrik Steffens

Henrich Steffens

1773 (Stavanger, Norway) – 1845 (Berlin)

Steffens brought a strong if highly individual scientific awareness to his philosophy, and was an important influence on Danish nationalism. He studied under the geologist Werner, but before that was a student in Jena, where he met the brothers Schlegel, Fichte, Novalis (who was stimulated by his zoological ideas) and Goethe (who failed to appreciate his work). He was a close disciple of one friend, Schelling, a colleague of another, Schleiermacher, and wrote an essay for a third, Runge. He knew the eccentric Ritter, influenced Ørsted (whom he admired) and Grundtvig, and changed Oehlenschläger’s life in a single meeting.

Wilhelm Weber

1804 (Wittenberg, Germany) – 1891 (Göttingen)

Chladni lived in the same house as Weber’s family, and inspired the teenager. Weber first met the older Gauss, who was responsible for his appointment to Göttingen, at Humboldt’s; they became good friends and collaborated closely for six years, setting up the world’s first telegraph, over 3km connecting observatory and university. Friedrich Kohlrausch (later an important collaborator), Siemens, and Riemann were all students of Weber’s, and Dirichlet another close friend and colleague (he took in Dirichlet’s children after both parents died suddenly). Weber met Fechner through his brothers, during his politically-related banishment from Göttingen.

Wilhelm Weber knew…

Gustav Kirchhoff

1824 (Königsberg, Prussia, now Kaliningrad, Russia) – 1887 (Berlin)

Kirchhoff made fundamental contributions to electrical-circuit theory, spectroscopy and black-body radiation, producing seminal work even while a student of the influential Neumann). He met his colleague, long-term collaborator and strong friend Bunsen when both were at Breslau, later following him to Heidelberg; Mendeleev, Meyer, Schröder, Auer von Welsbach, Kamerlingh Onnes and Roscoe were among their research students. Kirchhoff’s friend and former student Helmholtz ultimately enticed him to Berlin, where Planck (who admired him but found him dry) and Hertz also studied with him.

Heike Kamerlingh Onnes

1853 (Groningen, Netherlands) – 1926 (Leiden)

Kamerlingh Onnes led the world in low-temperature physics and discovered superconductivity. Bunsen and Kirchhoff taught him, while his close friend van der Waals’ theoretical work strongly supported his own practical research. Lorentz, a distant cousin, was also a close colleague at Leiden, where Ehrenfest also joined them. Dewar, Bohr and Langevin were all correspondents. The young Einstein wrote to Kamerlingh Onnes about a studentship, but got no reply; they later forged a close connection, Einstein enjoying frequent visits to Leiden, though he felt that Kamerlingh Onnes lacked skill at expressing his thoughts.

Heike Kamerlingh Onnes knew…

Hermann von Helmholtz

1821 (Potsdam, Prussia, now Germany) – 1894 (Charlottenberg)

Helmholtz is a towering figure in science, his work notable for its scope and vision. Mitscherlich and Müller both taught him, with Brücke and du Bois-Reymond fellow-students and lasting friends. He himself taught Planck, Hertz, König, Michelson and James; Hertz (happily) and Wundt (less so) became his assistants. He found his close colleague Kirchhoff extraordinarily clear-headed, Faraday as unaffected as a child. He drank “remarkably good wine” with Plücker. Magnus offered him research facilities when he was stuck in the army, while Humboldt hastened his release. Siemens was a lifelong close friend, whose son married Helmholtz’s daughter.

Hermann von Helmholtz knew…

Horace-Bénédict de Saussure

Bénédict de Saussure

1740 (Conches, Switzerland) – 1799 (Geneva)

A polymath, Saussure was a founder of geology (a word he coined) and of alpinism. He collected plant specimens for Haller, his mentor and friend. Bonnet got him to train for his ascent of Mont Blanc by climbing the stairs 8 or 9 times daily. He helped fund the Montgolfiers, and took temperature-readings inside their balloon. Volta inspired him. He met Guyton de Morveau in Dijon, Buffon in Paris, Franklin in London, and dined with Banks the evening before Bank’s departure on Cook’s voyage. Humboldt visited, after one of his cyanometers, and Jefferson offered him a post in Virginia when he’d fallen on hard times.

Horace-Bénédict de Saussure knew…

Henri-Victor Regnault

1810 (Aix-la-Chapelle, France, now Aachen, Germany) – 1878 (Auteuil, France)

Regnault made extensive contributions to 19th-century chemistry (he was the first to synthesise PVC, albeit accidentally) and physics (showing Boyle’s law to be only approximate), as well as contributing to the development of photography. He worked under Liebig, and was Gay-Lussac’s demonstrator at the École Polytechnique. He collaborated with Foucault on research into binocular vision, was a colleague of Biot’s, and wrote a comprehensive chemistry textbook, influential in both its French and German editions. Bunsen, Herschel and Airy were correspondents.