Wow, even for a Kirk McDonald "pedagogic diversion", there is a lot in footnote 4. There are scattered typos, but it's an excellent annotated bibliography. I

Wow, even for a Kirk McDonald "pedagogic diversion", there is a lot in footnote 4. There are scattered typos, but it's an excellent annotated bibliography. I was unaware of some of the 21st century papers it lists. A small thing, and it could just be me. I'm not sure where McDonald is going with respect to his point in footnote 7 about his reference [54] (Einstein 1911, https://onlinelibrary.wiley.com/doi/abs/10.1002/andp.19113401005 https://onlinelibrary.wiley.com/doi/abs/10.1002/andp.1911340... (German), https://einsteinpapers.press.princeton.edu/vol3-trans/393 https://einsteinpapers.press.princeton.edu/vol3-trans/393 (English)) and unfortunately his ...kirkmcd.princeton.edu/examples/GR/... links all want passwords. It's obvious that the footnote is about §2 of [54], but to me it does not really engage with the \gamma m in the text referring to footnote 7 (or indeed the content of your own comment's parent comment). Instead the (spring-balance-indicated, i.e. "contact"[1]) change of weight when light is beamed from one weighed system to another is diagnostic, with the focus of thought being on how that beamed light is adapted when acceleration or gravitation is relevant. This is further developed into gravitational redshift in [54]§3 (which, frankly, is an amazing bit of Einstein's early thinking). So I don't see how footnote 7 fits the perihelion precession topic, where the (rest) masses are defined as constant and radiation pressure is ignored. [The sodium quasi-cometary tail of Mercury is cool, though. <https://www.nature.com/articles/s41467-020-18220-2 https://www.nature.com/articles/s41467-020-18220-2>] [1] https://math.ucr.edu/home/baez/physics/General/Weight/whatIsWeight.html https://math.ucr.edu/home/baez/physics/General/Weight/whatIs...