History of the 13-inch photographic telescope and its use since the discovery of Pluto

Immediately after the discovery of Neptune, the possibility of a more distant planet became a valid field of interest. Stimulated by numerous unsuccessful approaches by others, Percival Lowell became interested in the problem. The background that led to the development of several observational programs based on his early theoretical study of all the observed comet orbits in Galle's catalog is outlined. From these experiences, Lowell's successors specified and constructed the 13-inch photographic search telescope. The use of the telescope for comet and minor planet work following the discovery of Pluto by Clyde W. Tombaugh in 1930 is described, followed by a summary of a 20-year program of proper motion studies by H. L. Giclas, utilizing the early planet search plates as first-epoch observations. Ancillary equipment developed to facilitate observations and reductions of measurement is described.