The work Enriques, Federigo, Prinzipien der Geometrie appeared in
"Ancyklop. der math. Wissensch." III, I,1,1, pp. 1-129, 1907.
It appears in the french translation of the Encyclopedy, under the
signature of Enriques himself as "Principes de la Ge/ome/trie", in Encycl.
des sciences math. III, pp. 1-147 whose year escapes me but must be between
1911 and 1915, I believe.
Francis Buekenhout