In the spring of 1913 Schmidt graduated from high school passing his final examination. Before beginning his university studies he attended courses over the summer of 1913 in mathematics, physics and chemistry at the University of Rostock. He then entered the University of Leipzig in the autumn of 1913 and began studying physics, chemistry, mathematics and philosophy. World events, however, were to have a major impact on Schmidt's university education. In July 1914 Austria-Hungary issued an ultimatum to Serbia and began to attack them on 28 July. Before the end of the month Russia had begun to mobilise its forces to attack Austria-Hungary and Germany issued an ultimatum to Russia. Both Russia and France began to mobilise on 1 August and German troops entered Luxembourg on the next day. Germany declared war on France on 3 August, German troops invaded Belgium which resulted in Britain making an ultimatum to Germany on 4 August; World War I had begun. The effect of the war on Schmidt was that, as a student with expertise in physics and chemistry, he was required to undertake war work. Part of this war work was for the army, and was carried out in the Physicochemical Institute of the University of Leipzig. He was still able to combine this war work with undergraduate lectures. His mathematics lecturers at Leipzig included Wilhelm Blaschke, Gustav Herglotz, Otto Hölder and Karl Rohn. His physics lecturers included Theodor des Coudres.
In 1918 Schmidt began undertaking research at the University of Leipzig, working towards his doctoral thesis. His thesis advisors were the physicist Theodor des Coudres and the mathematician Gustav Herglotz. He submitted his theoretical physis thesis Über die Möglichkeit und Stabilität von Gleichgewichtszuständen ruhender sowie rotierender Elektronengruppen innerhalb einer im allgemeinen nichtäquivalenten Kugel von homogener positiver Elektrizität to Leipzig in 1919 and graduated Dr phil on 11 April. He taught in the high school at Altona from 1919 to 1923 and during this time, on 16 December 1921 he married Johanna Fernholz from Bochum. A daughter Irmgard was born on 9 August 1923 and a second daughter Gertrud was born in 1927.
Schmidt published a number of important books between 1920 and 1922, in German, English and Italian. In 1920 Das Weltbild der Relativitätstheorie. Allgemeinverständliche Einführung in die Einsteinsche Lehre von Raum und Zeit appeared while Zahl und Form. Leichtfassliche Einführung in die Mathematik was published in 1921. Also in 1921 Weltäther, Elektrizität, Materie. Physikalische Fragen der Gegenwart was published as was the English text Relativity and the universe. A popular introduction to Einstein's theory of space and time. In the following year the Italian text La prima conoscenza della relatività dell' Einstein alla porta di tutti was also published.
In 1923 Schmidt was appointed as professor at the polytechnic institute in Koethen where he remained until 1937. During this time he published the book for which he is best known internationally, namely his work on the aerodynamics of flight Aerodynamik des Fluges. Eine Einführung in die mathematische Tragflächentheorie (1929). Another major publication during these years was his introduction to the theory of the wave equation Einführung in die Theorie der Wellengleichung (1931). He submitted his habilitation thesis to the University of Leipzig on 8 May 1926, becoming a privatdozent. He was appointed as an extraordinary professor of mathematics at the University of Leipzig in 1933. Of course this was the year in which there were huge political changes in Germany. Hitler came to power in 1933 and within a year had proclaimed himself Chancellor and Führer of the German Reich. Germany had no air force since it was forbidden under the 1919 treaty of Versailles signed after World War I. Hitler now ordered the creation of a German air force and began to rapidly expand the army and navy. In January 1935 he regained the Saar region by holding a plebiscite, and in March 1936 German troops entered the Rhineland. In August 1936 two year conscription was declared in Germany. From August 1937 Schmidt was employed as a ordinary professor for mathematics in the service of the Reich, working at the aviation laboratory in Berlin-Adlershof.
This was a difficult period for Schmidt, for his wife died on 22 April 1941. He then employed a housekeeper to look after his home but by the beginning of 1943 Berlin began to be bombed by the British. The first daylight raid on Berlin took place on 30 January 1943. Schmidt's home was destroyed in a bombing raid in August, before the Battle of Berlin which began in November and saw sixteen bombing raids over the winter of 1943-44. For a while after his home was destroyed Schmidt lived with friends in Berlin but in December he found a house in Koethen (Anhalt). He continued to work at the aviation laboratory in Berlin until the end of the war. Germany surrendered in May 1945 and Allied forces entered Berlin on 12 July. Schmidt's employment at the aviation research laboratory came to an end. While he was working at the laboratory Schmidt published, jointly with Kurt Schröder, a comprehensive report on the theory of laminar boundary layers deals with the basic conceptions and equations Laminare Grenzschichten. Ein kritischer Literaturbericht. I. Teil. Grundlagen der Grenzschichttheorie (1942). It is worth noting that one of the main features of the report is the fact that it presents the material in a more rigorous way than usual. To get an idea of what was in this major report we give the section and chapter headings:-
1. The equation of continuity, the impulse theorem and the Navier-Stokes equations.
2. The equations of motion in orthogonal curvilinear coordinates.
3. Parallel curves and normals of a plane arc as coordinate lines.
B. Introduction of the boundary layer equation:
1. The procedure of Prandtl and Blasius.
2. Complements and generalizations.
3. A systematic study of the neglections made in boundary layer theory.
4. A rigorous solution of the Navier-Stokes equations as an example.
C. The assumptions of von Kármán and Pohlhausen:
1. Kármán's stream function.
2. Pohlhausen's modification of Kármán's assumption.
3. Kármán's integral condition.
D. The theory of von Mises:
1. The fundamental equations.
2. The analogy with heat conduction.
3. The equations of a steady two-dimensional motion with respect to the stream lines and their orthogonal trajectories.
E. Related ideas:
1. A remark of Jeffreys.
2. R H Smith's theory of the boundary layer based on a minimum principle.
3. Klose's conception of the boundary layer theory as part of a theory of fluids with vanishing viscosity.
After Schmidt died his colleagues completed the manuscript he was writing giving an introduction to vector and tensors. This was published as Einführung in die Vektor und Tensorrechnung unter besonderer Berücksichtigung ihrer physikalischen Bedeutung (1953). The first two chapters give a clear exposition of the elements of vector algebra and calculus with some physical applications. The third chapter deals briefly with tensors as vector triples and as matrices, using the stress tensor as an illustration.
Article by: J J O'Connor and E F Robertson