The paper presents a formal description and contents' analysis of Wincenty Lutoslawski's unpublished thesis entitled 'Aesthetisches Studium. Ueber das phonetische Element in der Poesie' drawn up yet in the undergraduate period. The main topic of Lutoslawski's study is the scientific research focusing on searching for the universal rhythmical patterns in poetry and in other versified texts. He undertakes a simple research procedure, which borrows some methodological rules from natural science, and this is probably connected with a fact that he studied chemistry and physics for about two years before he definitely returned to philosophy. For each historian of science Lutoslawski's work seems to be very much valuable, and especially because of the fact that the great scholar's output remains unknown. Undoubtedly, from a purely scientific point of view it is also significant, because the essential conceptions and postulates of the stylometric method that were presented in his work entitled 'The Origin and Growth of Plato's Logic..., harmonize with his early writings.