Kohau rongorongo studies began early in the 19th century but the first fundamental work devoted solely to the Rapanui script appeared only in 1958, in the book by German scientist, Thomas S. Barthel (Grundlagen zur Entzifferung der Osterinselschrift) in which the author published the results of his research conducted between 1953-56. In spite of the fact that Barthel remained firm on his original point of view on the character of the Rapanui script (a proto-script as stated by N. N. Mikloukho-Maklay but in "telegraphic" style), his work until now is the basis for the study of Easter Island texts.
Fedorova, Irina K.
"About One Glyph of kohau rongorongo,"
Rapa Nui Journal: Journal of the Easter Island Foundation: Vol. 11
, Article 4.
Available at: https://kahualike.manoa.hawaii.edu/rnj/vol11/iss4/4