The most observed object by far was M42 (the Orion Nebula) which was imaged on at least 148 of 406 plates ranging in epoch from January 5th, 1897 to March 2nd, 1922. We believe this may have been a program for monitoring the nebula supervised by Dr Francis Preserved Leavenworth since he published several articles on the subject in the Astronomical Journal. Leavenworth once reported finding a new star in the Orion Nebula and then retracted the claim shortly thereafter. (Unfortunately the controversial plates are no longer in our collection.) We also know from his published work that Dr Leavenworth conducted a great deal of non-photographic work with the 10" Refractor using a micrometer to measure double stars.
The 23 plates of M57 (the Ring Nebula) from April 28th, 1897 to October 24th, 1913 were probably part of a program supervised by Dr Burt Leroy Newkirk. We believe he may have been attempting to measure the geometric parrallax of M57.
There are also a series of 35 plates taken of Nova Geminorum (DN Gem; HD 50480) between August 4th, 1912 and April 24, 1919 which we believe were meant to measure the decline in brightness for this object from its outburst in 1912. However, we can find no record that this data was ever published except for a note in Astronomische Nachrichten about its position.
The ten (10) plates of asteroids, sixteen (16) plates of comets, and forty four (44) plates of nearby/high proper motion stars, were probably taken for astrometric purposes. Many of these plates have been marked on the non-emulsion side of the plate to note the location of reference stars as one might do prior to measuring the relative positions on a plate. And Dr Leavenworth, William Otis Beal, and Alfred Davis all published papers in the Astronomical Journal reporting the positions and orbits of comets and asteroids using photgraphs made with the 10" Refractor.