"he geometric series 1 + z + Z 2 q " . . . converges in the I disk Izl < 1, and its partial sums 1 + z + z 2 + . . . + z '7 have zeros at the (n + 1)st roots of unity, except at the point 1 itself. In particular, every point on the circle of convergence Izl = 1 is a cluster point of zeros of the partial sums. In his Doctoral Dissertation of 1914 in Berlin, Robert Jentzsch gave a sweeping general izat ion of this fact. The remarkable theorem of Jentzsch says that for a n y power series a0 + a l z + a 2 z 2 + . . . with finite and positive radius of convergence, every point on the circle of convergence is a cluster point of zeros of the partial sums. It is a striking result, included in classical texts such as Landau [24], Dienes [25], and Titchmarsh [26], and it deserves to be better known than it seems to be today. Jentzsch obta ined other substantial results, notably a cont inuous analogue of the Perron-Froben ius theorem and a theorem on power series that arose from work of Hurwitz and P61ya [28], but after a few years his publicat ions ceased. We wonde red what had become of him, and soon ascertained [1] that he was a casualty of World War I, kil led in battle in 1918. Interested to learn more about this talented young mathematician, we began to investigate. From the c u r r i c u l u m v i t a e in his dissertat ion [J4] and other sources [2, 3], we were able to assemble a fairly comple te personal history. Robert Jentzsch was born in K6nigsberg on November 4, 1890, the younges t in a family of four children. In his c u r r i c u l u m v i t a e , he identifies himself as a Lutheran. His father, AlfredJentzsch (1850-1925), was a dis t inguished professor of geo logy in K6nigsberg, later in Berlin, and a wellknown conservationist. Robert 's o lder brother Felix Jentzsch (1882-1946) had a product ive career as a physicist, specializing in optics; he was a professor in Giessen and in Jena. Their sister Martha (born 1885) marr ied Richard Scholz, who became a professor in Leipzig and an authority on early Church history [2]. Another sister Edith (born 1887) marr ied Robert Chavoen, an engineer who was product ion manager of a coal-mining company [2, 19]. Robert 's mother Clara Falkson was the daughter of Ferd inand Falkson (1820-1900), a Jew in K~3nigsberg who married a Christian w o m a n named Friederike M611er in 1846. Prussian law did not specifically prohibi t "mixed marriages", but the couple were unable to find a minister in K6nigsberg who was willing to perform the ceremony. Falkson sent complaints to the government and even to the King of Prussia, all to no avail. As a last resort, the couple trave led to England with the br ide 's father and were married there [5, 6]. Upon return to K6nigsberg, they faced a legal chal lenge to the validity of their marriage, and a long court
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