Mars.
P. [160].—Prof. W. H. Pickering observed some of the canals on Mars in 1890 with a 12-inch refractor, but was not able to double any of them. He says that, in examining these objects, the power employed should not “exceed one or two hundred.” This is quite contrary to the advice of others, who recommend high magnifiers; and perhaps it accounts for Prof. Pickering’s failure in recognizing the duple canals.
With the great 36-inch refractor Mr. Keeler saw, on July 5 and 6, 1890, some curious white spots on the edges of the gibbous limb of Mars, something similar to those visible on the unilluminated part of the lunar disk. The canals were observed as feeble diffused bands. The two satellites were seen by a lady visitor, though previously unaware of their existence.
P. [161].—The method of deriving the rotation-period of Mars is exemplified by Mr. Proctor in the ‘Monthly Notices,’ vol. xxviii. p. 38. An interesting paper, “On the Determination of the Rotation-Period of Jupiter in 1835,” will be found in the ‘Memoirs,’ vol. ix.
Planetoids.
P. [167].—The 308th planetoid was discovered by Charlois on March 5, 1891.
Jupiter.
P. [170].—Dupret, in Algiers, saw Jupiter with the naked eye on Sept. 26, 1890, and following days, twenty minutes before sunset.
P. [191].—M. Guillaume, during a recent transit of the shadow of Jupiter’s second satellite, observed a duplicate shadow, fainter than the ordinary one, which partly covered its southern side.
Comets.