The Dominance of alright/all right in the 30s and 40s

Recently, I have been reading books written in the 30’s and the 40’s and something that came to my attention was the frequency of “alright/all right” in them. So I did the next step to investigate my suspicion and used Ngram to see if by any chance my observation made any sense. Well this is what I got.

Obviously, it is not a definitive evidence, but it seems that “all right” was much more popular in the written English of the early 20th century.