"For a long time no mind dared to touch the problem. At length a young astronomer rises, unknown to fame, but with a mind capable of grasping all the difficulties involved in any of these questions. I refer of course to LEVERRIER. He began by taking up the movements of Mercury. He was dissatisfied with the old computations and the old tables; and he ventured to begin anew, and to compute an entirely new set of tables. With these new tables, he predicted the _precise instant_ when the 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.