He had been inspired by the director of the Cologne Observatory, Hermann Klein,[1] to make the study and observation of the Moon his life's work.

For this purpose he obtained a series of low-resolution negatives of the lunar surface that had been taken at the Lick and Paris observatories.

His illustrations of the Moon were made in charcoal, graphite pencil, and ink, and were considered superior to any previously produced lunar maps in their accuracy and level of detail, and continue to be considered works of art.

However his health had suffered, possibly due to his long nightly labors at his telescope.

About 10 years following his death, his remaining drawings and sketches were published in a second volume by the Austrian selenographer Rudolf König.