planet Mercury, on the 18th of May, 1845, would touch the sun, and
sweep across it. The time rolls round when the planet is to be seen,
and his prediction verified or confuted. The day arrives, but, alas!
for the computer, the clouds let down their dark curtains, and veil the
sun from his sight. Our own Observatory had just been finished; and if
the audience will permit, I will state briefly my own observations upon
the planet. I had ten long years been toiling. I had commenced what
appeared to be a hopeless enterprise. But finally I saw the building
finished. I saw this mighty telescope erected,--I had adjusted it with
my own hands,--I had computed the precise time when the planet would
come in contact with the sun's disk, and the precise point where the
contact would take place; but when it is remembered that only about the
thousandth part of the sun's disk enters upon the field of the
telescope, the importance of directing the instrument to the right
point will be realized. Five minutes before the computed time of the
contact, I took my place at the instrument. The beautiful machinery
that carries the telescope with the sun was set in motion, and the
instrument directed to that part of the sun's disk at which it was
anticipated the contact would take place. And there I sat, with
feelings which no one in this audience can realize. It was my first
effort. All had been done by myself. After remaining there for what
seemed to be long hours, I inquired of my assistant how much longer I
would have to wait. I was answered _four minutes_. I kept my place for
what seemed an age, and again inquired as before. He told me that but
one minute had rolled by. It seemed as if time had folded his wings, so
slowly did the moments crawl on. I watched on till I was told that but
one minute remained; and, within sixteen seconds of the time, I had the
almost bewildering gratification of seeing the planet break the
contact, and slowly move on till it buried itself round and deep and
sharp in the sun.

"I refer to this fact for two reasons,--first, to verify Leverrier;
and, second, to impress upon your minds the desirableness of locating
our observatories in different parts of the earth. No European
astronomer could have made this observation, because in their
longitudes the sun would have set previous to the contact of the planet
with its disk. I had the gratification of furnishing these observations
to Leverrier himself, who reported upo