I know that I can say like this:
"Dr. Thomson paid them a visit."
Is this sentence correct:
The author tries to elucidate, in his book, what Dr. Thomson saw and did not see during the visits he paid to them (a group of experimenters).
I know that I can say like this:
"Dr. Thomson paid them a visit."
Is this sentence correct:
The author tries to elucidate, in his book, what Dr. Thomson saw and did not see during the visits he paid to them (a group of experimenters).
The sentence is grammatically correct, and would sound perfectly natural, but if the visits have been discussed earlier, it might be better to write:
In his book, the author tries to elucidate what Dr. Thomson saw and did not see during his visits.
(I moved the prepositional phrase to the beginning; I think it sounded better there. Also, you have two "he"s in the sentence, the author and Dr. Thomson. You might want to recast the sentence to avoid that.)