MicroscopyPioneers
Te son of a lawyer,
Kirchhoff was born and educated in Königsberg, Prussia (now the Russian city
Kaliningrad). He
graduated from Albertus University in 1847 and soon aſter married Clara Richelot,
the daughter of
his mathematics professor. Te couple immediately relocated to Berlin, where Kirchhoff had obtained an unpaid teaching position. In 1850, at the unusually young age of 26, he
re- as Professor Extraordinarius
ceived an appointment in Breslau (now Wroclaw),
Poland. In Breslau, Kirchhoff became acquainted with Bunsen, who urged Kirchhoff to follow him to Heidelberg, Germany, which he did in 1854. As a professor of physics at the university there, Kirchhoff was very successful, but he did suffer personal adversity when his wife died in 1869, leaving him alone to finish raising their four children, a task made more difficult by a disability that oſten confined him to a wheelchair or to the use of crutches. He remarried, however, in 1872 to Luise Brömmel, and his family remained in Heidelberg until 1875, at which point his failing health inspired him to accept the chair of mathematical physics at the University of Berlin because experimental work was becoming increasingly difficult. Most of Kirchhoff’s early research was related to electrical
currents. While still only a graduate student, he published a paper that included a pair of rules for the analysis of circuits, which are widely used in the field of electrical engineering and are now known as Kirchhoff’s laws of circuits. Ten, by 1850, Kirchhoff determined that Georg Ohm’s suggestion that electrical flow is analogous to the flow of heat was incorrect and misleading, lending itself to the mistaken assumption that a static current could be present in a conductor. Kirchhoff made another important contribution in this area around 1857, when he noted that an electrical current traveled at approximately the
same speed as light. However, he did not make the connection, which was deduced by James Clerk Maxwell in 1862, that light was an electromagnetic phenomenon. Kirchhoff’s important work on thermal radiation was
primarily carried out in the late 1850s and early 1860s. In 1859, his studies led him to propose what is commonly referred to as Kirchhoff’s law in thermodynamics. Proven in 1861, this law holds that at thermal static equilibrium, the emissivity of an object or surface is equivalent to its absorbance at any given wavelength and temperature. In the course of his studies of radiation, Kirchhoff coined the term black body to describe a hypothetical perfect radiator that absorbs all incident light and, therefore, emits all of that light when maintained at a constant temperature in order to preserve equilibrium. Te concept of black body radiators is key to the determination of color temperature in the field of photography, but even more importantly, questions raised about black body radiators could not be explained using traditional views of statistical mechanics and electromagnetism. In his attempts to solve these problems, Max Planck made history by discarding contemporary scientific notions and hypothesizing that a black body radiator could only absorb or emit energy in the form of packets he called quanta. In addition to formulating laws of electrical currents
and thermal radiation, Gustav Kirchhoff developed a spectroscope with Robert Bunsen, and the pair pioneered the field of analytical spectroscopy (the study of the emission and absorption of light and other radiation by matter in terms of
their relationship to the wavelength of the radiation).
Underlying this achievement was Kirchhoff’s demonstration in 1859 that all pure substances display their own characteristic spectrum. Prior to that time, other scientists had postulated that each element had a unique spectrum, but impurities in their samples impeded the discovery because they resulted in the appearance of multiple spectra simultaneously. Equipped with this knowledge, Kirchhoff and Bunsen discovered the elements cesium and rubidium, analyzed the chemical composition of the sun, and explained the dark lines in the solar spectrum generally referred to as Fraunhofer lines—an achievement oſten considered an important turning point in astronomical studies.
56
www.microscopy-today.com • 2011 September
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84