He wrote a great book about his trip, prizing amazing African nature and giving a hard time colonial powers for making this continent such a miserable living place for its natives. Book does not have English translation unfortunately.
Nowak died soon after coming back (trip was really exhausting, he got Malaria) and for many years his achievement was forgotten. In 1962 his daughter managed to publish a book her father trip, but it didn't attract much attention (communists didn't like to promote anything positive about pre-communism times achievements). Finally it was reedited in 2000 and become very popular in Poland.