This is an interesting paper. It provides a detailed overview of lives and works of the two Thiems. As such, I do think the text can be published - but only once a few issues have been resolved. These issues relate generally and most importantly to the balance and construction of the historical argument.

Let me start with a detail. In the abstract, it is suggested that it is "remarkable" that the Thiems did their theoretical work while not in university. I would argue that this is an odd statement, as not that many engineers at the time worked at universities, but many did discuss all kinds of issues in the scientific/professional journals. This may seem a detail indeed, but it may represent two issues that needs to be addressed.

Issue 1 relates to the more general context of the Thiems, as engineers and theorists. They were not alone at the time, but we do not really get an idea on that from the paper. The two Thiems lived in different times, did that matter for their work? I would strongly suggest that some ideas on engineering professionalization need to be included, to provide a more general context to understand the Thiems in their time. If needed, I can provide a few publications that are worth using.

Issue 2 relates to the general claim the authors make. Apparently, the Thiems made clear and important contributions - line 23 claims they "laid the foundations" for much. In the text, however, we either find that they modified existing things, or we read in rather speculative terms that "it is very likely" (line 362) or "probable" (line 369). This is one example that for me shows that the fame of the Thiems is not that clear at all. I am sure they worked on much and left many texts, but that in itself is not enough evidence.

These issues are not that difficult to solve, I would think. After all, this text does not need any speculative claim at all to show that the Thiems are interesting persons, who have done much. They do appear in recent text books (please also include these in the Intro, when this statement is already made), but who were they? That is an interesting read in itself. The authors should check their own text for too optimistic claims, but once this is done, there is enough to enjoy!

A few last remarks complete my suggestions:

Why do we read so many direct quotes, with many from the archives, between lines 692-841? It makes the text as a whole unbalanced, and creates the question why these letters are so important? I would recommend explaining this better or rewrite part of the text.

In any case, all direct quotes need to have a full reference. Archival material needs to be provided in the references too, and needs to have citations in the text too. In the historical science, it is practice to list archival material in a separate list, and cite in foot notes. Archival material, after all, is not a regular secondary source. What we read in lines 727-732 needs to be in the archival list. If I can assist in how to do that, please let me know.

Please do not use language like Thiem "instinctively" understanding something (line 364). I would like to see that such remarks are all removed.

All in all, there is still some work to be done on this paper, but as I think it is quite doable, and the text as such is rather interesting and does not need too much speculation, I decided that these changes would qualify for "minor revisions". I look forward to the revised version.