"Opinions on Physics" are these among others, George Couvalis in Philosophy of Science, Sci. and Obj., 1997 on "indirect observation", p. ... Well, since my living is in this state, I can recommend you to look up indirect observation in every introductory book to Philosophy of Science, especially those from the 90s and further back in time.
I've been thinking the book has held a point on "indirect observation" for separating "scientific realism" from other types of "realism", one of which is "realism", rather old fashioned now. But as the story goes, I think my books are being tampered with because the index listing of "indirect observation" is gone as well as the instance of "Casui Studies", 1 page, in Research Designs and Methods. Sorry. I'm being sabotaged!
The other is my further work on "indirect observation", being indirect observations that are there by laws of nature, i.e., if you see only half the planet, the other half of the planet has to be there because... and this is found with "The Power of a Single Span of Time - an Instance - Contrary to Hume on Induction - The Refutation of the Problem of Induction" and a smaller writing with the Scribblings file where this proceeds as a shorter writing.
It says on the SAGE publications website that the book should be 224 pp. Mine (now) is 195 before Ref. and Index and 206 and last paged page. (Leaving only 4 pages for the binding.)
There are some pages in addition, as some count the preface pages, viii, that is, 8 pages more to this book. But all in all, the book still falls short 2 pages compared to the 224 pp.
Indirect observation usually relates to viewing something through a magnifying scope/using a magnifier and using a telescope. One has through the times questioned everything that hasn't been seen with the naked eye. Even then, scientific realism or other versions of it, probably has 99.9 % following, even 100 % if one counts only the serious. In opposition, the philosopher gamers, the rogues, they who are in it for the hair splitting and making idiotic points. Just so you have it.
You can compare "indirect observation" with "instrumentalisation" where the data are gathered by the output of the instrument in use by itself and where no direct human sense can perceive. I guess examples of instrumentalisation can be measuring of mass and acidity. You can check it out yourself.
The magnifier is also the microscope. I'm not sure to what extent the magnifying _glass_ has been or is questioned, but realism, as above, has usually related to the naked eye as a starting point for human scientific investigation (and doubting everything else...)!
From Facebook where it has been originally posted!