the opposition of Mars which brings that planet nearest to us. As is
well known to astronomers, the perihelion of Mars is in the same
longitude in which the earth is on August 27; and when an opposition
occurs near that date, the planet is only 35 millions of miles from the
earth, and this is the closest approach which their bodies can ever
make.

Our magnetic receiver had been placed in position, the Morse register
was attached; the whole apparatus was in one of the upper rooms of the
observatory, in proximity with the telescope through whose glass for
days we had watched the approach of our sister planet. As the night
settled down upon us we had taken our seats for a few instants at a
table in a lower room engaged in one of those innumerable desultory
talks upon our project and their, even to us, somewhat problematic
character. Everything connected with that evening, apart from its having
been carefully recorded in my diary and notebooks, is very distinctly
remembered by me. I recall my father reading from a letter to Nature,
May 15, 1884, by Mr. W.F. Denning, discussing "The Rotation Period of
Mars." From my note-book I find the passage literally transcribed:

It read--"Notwithstanding his comparatively small diameter and its slow
axial motion, the planet Mars affords especial facilities for the exact
determination of the rotation period. Indeed, no other planet appears to
be so favorably circumstanced in this respect, for the chief markings on
Mars have been perceptible with the same definiteness of outline and
characteristics of form through many succeeding generations, whereas the
features, such as we discern on the other planets, are either temporary,
atmospheric phenomena, or rendered so indistinct by unfavorable
conditions as to defy measurement and observation. Moreover, it may be
taken for granted that the features of Mars are permanent objects on the