AbstractThe importance of laboratory instruments as sources for the writing of the history of psychology is stressed, and illustrated through the use of examples where their study has been profitable. Most importantly, the role of the Hipp chronoscope in the reaction‐time experiment is discussed, and the importance of various changes introduced into its design by James McKeen Cattell is shown. A photograph, first exhibited by the Department of Psychology of Clark University at the 1893 World's Columbian Exposition in Chicago is included, and further illustrates the importance of these instruments to historian