Alexander Pogo was an astronomer and classical scholar born in Russia in 1893. He was an associate of George Sarton and then after his career at Yerkes Observatory at the University of Chicago became the librarian for the Mount Wilson Observatory in Pasadena, California. The letter by his associate is signed but we have not been able to identify. The Yerkes Observatory and its assets have been transferred from the University of Chicago to an association which will open in the Fall of 2020. This letter also deals with a paper written by Paul Bourgeois and Jacques Cox at Bruxelles which has discarded their hypothesis that the periastra depend upon the orientation of the larger galactic system. he goes on to explain that while they had expounded the idea cautiously, the Belgian writers had treated it as if they were showing it as pure science. The key idea he states is their desire to discard the [Franz] Kounitzky idea of variable velocity of light. He notes there was an article in C.R. by Salet who not only alludes to their theory (but Salet sent him an offprint of it!). The next few paragraphs discuss how to discuss the matter with the Belgians using the technological language of astronomy (pseudo-Cepheids, ordinary binary and variations in light. Paul Bourgeois is expected at Chicago in a few weeks. He mentions also Pogo's time with Albrecht Unsoeld. He notes that the ladies Parkhurst and Company are on a trip. Signed Handwritten notes at the bottom of the letter cite the French work by Bourgeois and Cox as well at another work which appeared in 1929. He does not mention Bibliographie rapide de l'astronomie by them (one copy recorded at Duke University Library). The Huntington holds 936 items in Pogo papers. While the letter is full of content, it will require further identification by someone expert in the history of astronomy in the early 20th Century to determine ifs full significance.