In Chapter I.9 of Chandler-Magnus "The History of Combinatorial Group Theory", a number of important mathematicians in the early history of the development of group theory and sources for their obituaries are given. For example, we certainly find an entry **Dehn, Max, 1878-1951**. For other names, less information is known, such as **Pick, G., 1859-1943(?)**. This latter question mark reflects the fact that Georg Pick died in the Theresienstadt concentration camp in 1942, and finding this information might have been difficult at the time of the writing of the book (1982).

All names in this list have a source for where their obituary may be found, and at least one of a birthyear or death year is present -- except for one name. This name is listed simply as **H. Vogt: ?-?.**, with no further information. Curiosity piqued, this gives my question:

**Who was H. Vogt? What were his mathematical contributions?**

Here's the clues I've got this far. The most relevant piece of information is the following paper:

*Vogt, H.*, Sur les invariants fondamentaux des équations différentielles linéaires du second ordre. , Ann. Sci. École Norm. Sup. (3) 6 (1889), 3–72. (Thèse, Paris),

This paper is the only paper cited by Chandler and Magnus for Vogt, and is hence the only publication I am certain is by the desired H. Vogt. It also appears to have been his Ph.D. thesis. No result can be found on Mathematics Genealogy matching this.

There are a number of matches on MathSciNet for publications by an H. Vogt; the earliest is from 1879, by a Heinrich Vogt, and this could in principle be the same H. Vogt as above. The latest that could conceivably be by our H. Vogt is from 1923 -- this is again on differential equations, so seems very likely to be by the same author!

This would give a (very!) rough idea of (1860-1930) as the lifespan of our dear H. Vogt -- perhaps this helps the search.

One idea is that H. Vogt could possibly be related to (father of?) Wolfgang Vogt, a young German mathematician whose last paper was in 1914, and who may well have perished, as did so many other young German academics at the time, in World War 1, such as Werner Boy, of Boy's surface fame, and Hugo Gieseking. The topic of his 1906 Ph.D. thesis seems -- at least on a surface level -- somewhat related to what H. Vogt did, especially if some of the other publications on MathSciNet were by the same H. Vogt.

Note: there is a 1932 paper by someone called H. Vogt, namely *Vogt, H.*, **Max Wolf.**, Astronomische Nachrichten 247, 313-316 (1932). ZBL59.0039.09. However, this seems to be by the nazi astronomer Heinrich Vogt (1880-1968), who seems unrelated (and likely did not write an article about differential equations at the age of 1).

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