Ph.D. Lineage for Robert A. Cohen

Since Henry Rowland never received a formal Ph.D., the lineage officially stops there. However, according to Wikipedia, Rowland spent a short time as a student with Hermann von Helmholtz (1821-1894) just prior to joining Johns Hopkins University. According to his biography, Helmholtz completed his dissertation in physiology at the Medical Institute in Berlin, graduating in 1843. He eventually became professor of physics at the University of Berlin. According to Wikipedia, Helmholtz' advisor was Johannes Peter Müller (1801-1858), who was at the Humboldt University of Berlin at the time of Helmholtz' graduation. According to Wikipedia, Müller received his M.D. at the University of Bonn under Philipp Franz von Walther, followed by studies at the Humboldt University of Berlin, where he worked with Karl Rudolphi. Wikipedia doesn't have information on von Walther's advisor but does have information on Rudolphi. Following the lineage through Rudolphi, we have the following: Leibniz' advisor is unknown. More is known about Leibniz' son, Gottfried Leibniz (1646-1716). According to this biography, after receiving his doctorate at the University of Altdorf in 1667 (with his dissertation On Perplexing Colors), Gottfried Leibnitz studied mathematics and physics under Christian Huygens beginning in 1672. The Mathematics Genealogy Project also lists Leibnitz as Huygens' student, and in turn lists two advisors for Huygens: Frans van Schooten, Jr. and Jan Jansz Stampioen, Jr.. The latter's advisor is unknown but two are listed for the former. The furthest this goes back is to Gregory Palamas (1296-1359), a monk in Greece. Most of the above is also included in the Academic Tree list.