Other astronomers later showed that Jupiter’s main moons are tidally locked and rotate synchronously with their planet like our Moon. In his subsequent 1897 paper, Douglass appears more certain of the key markings he described: “On February 20th … an interval of extremely good seeing revealed the Great Northern Belt in longitude 260° to 20°, with perfect distinctiveness and definition.”
In sharp contrast to Douglass and Pickering, Barnard’s drawings of Ganymede and Callisto show far more diffuse features: “Though conspicuous enough, they were so vague in form that at no two times was it possible to say definitely that the same marking was under observation.” He goes on to say, “I have been very much interested in Mr. Douglass’ paper on the third and fourth satellites of Jupiter.” After Barnard mentioned that he used the much larger 36-inch Lick refractor to make his observations, he wryly added, “According to Mr. Douglass’ drawings and statements, he finds these satellites covered by a series of fine dark lines, the maximum width being estimated at less than 0.1" or 200 miles. In appearance, from the drawings, these markings very much resemble those seen at the same observatory upon Mars, Venus and Mercury.”
These strident comments, well documented in William Sheehan’s memorable biography of Barnard, The Immortal Fire Within, point to the rivalry and disagreements between the two observatories. They were most glaring with respect to the putative martian canals and similar features as depicted by Percival Lowell and others. Much of the divergence hinged on Lowell’s claims that while his telescopes were of smaller aperture, seeing conditions at the high and dry elevation of Mars Hill were unequaled.
To that, Barnard countered that it was his belief that no existing telescope, except the 40-inch Yerkes refractor, “is so capable of showing the surface features of these satellites as the Lick 36-inch. I also believe there are brief intervals of good seeing at the Lick Observatory which are not excelled if indeed they are equaled at any other observatory.”