[Footnote 125: _Transactions of the American Society of Mechanical Engineers_, 1954, vol. 76, pp. 483-492. See also _Transactions of the American Society of Mechanical Engineers_, 1955, vol. 77, pp. 853-861, and 1956, vol. 78, pp. 779-787.] The proper role of rational methods in the synthesis of mechanisms is not yet clear. "While we may talk about kinematic synthesis," wrote two of today's leaders in the field, "we are really talking about a hope for the future rather than a great reality of the present."[126] When the mental equipment and the enthusiasm of scholars who are devoting their time to the problems of kinematic synthesis are considered, however, it is difficult to see how important new ideas can fail to be produced. [Footnote 126: R. S. Hartenberg and J. Denavit, "Kinematic Synthesis," _Machine Design_, September 6, 1956, vol. 28, pp. 101-105.] An annual Conference on Mechanisms, sponsored by Purdue University and _Machine Design_, was inaugurated in 1953 and has met with a lively response. Among other manifestations of current interest in mechanisms, the contributions of Americans to international conferences on mechanisms reflects the growing recognition of the value of scholarly investigation of the kind that can scarcely hope to yield immediately tangible results. While we look to the future, one may ask how a lengthy view of the past can be justified. It seems to me that there is inherent in the almost feverish activity of the present the danger of becoming so preoccupied with operational theory that the goals may become clouded and the synthesis (let us put it less elegantly: the design) of mechanisms may never quite come into focus. If one knows nothing of the past, I wonder how he can with any confidence decide in what direction he must turn in order to face the future. Acknowledgment I am grateful to Professors Richard S. Hartenberg and Allen S. Hall, Jr., for reading the manuscript, making helpful comments, and suggesting material that I had not found. The errors, however, are mine. Additional References The following list of additional reference material on kinematics may be of help to readers who desire to do independent research. The material is listed according to the section headings in the text of the present article. TO DRAW A STRAIGHT LINE KEMPE, A. B. _How to Draw a Straight Line._ London, 1877. Contains a useful bibliography. Reprinted in _Squaring the Circle and Other Monographs_, New York, Chelsea Publishing Company, 1953. Much attention has been given to straight-line mechanisms since the time of Kempe; at least a half dozen articles have appeared in the United States since 1950, but I did not investigate the literature published after 1877. SCHOLARS AND MACHINES BECK, THEODOR. _Beiträge zur Geschichte des Maschinenbaues._ Berlin, 1899. Reviews of early works, such as those by Leonardo da Vinci, Biringuccio, Besson, Zonca, etc.