Close friendships were formed with some of our most prominent men, like Prescott and Ticknor. Lyell visited the great lakes, and compared the supposed ancient boundaries of Lake Ontario, when it was one hundred and fifty feet higher, with its present shore. He made a careful study of Niagara Falls, which cuts its deep gorge toward Lake Ontario, for seven miles, and estimated that it wore away a foot a year. If so, he argued that at least thirty-five thousand years have passed since the river began to cut its passage between the high rocky walls. "What would I give," said Lyell, "for a daguerrotype of the scene as it was four thousand, and again forty thousand years ago! Even four centuries would have been very important." Authorities differ as to the rate of the recession of the falls. Some estimate an inch instead of a foot yearly, requiring a period of more than four hundred thousand years. In 1845, Lyell published his "Travels in North America, with Geological Observations," and in September of the same year, returned again to our country, spending nine months in travel and study, and bringing out later, in 1849, his "Second Visit to the United States of North America." Already his "Elements of Geology" had appeared, which went through several editions. A seventh edition of the "Principles" had been published. He had also been knighted by the Queen, for his rare scholarship. Honored at home and abroad, working ardently and earnestly, often with failing sight, he had already won for himself the eminence of which he had dared to dream years before. Of course he was welcomed at all great gatherings. Macaulay and Hallam, Milmore and Mrs. Somerville, Rogers, and scores of others were often at his home. In 1851, he was appointed one of the Royal Commissioners for the first Great Exhibition held in Hyde Park, London, and a year later gave a second course of lectures at the Lowell Institute, Boston. So kindly and cordially had he written concerning us and our country, that he received the heartiest welcome. He had carried out in his life what he wrote to beautiful Mary Horner, twenty years before: "I hope we shall both of us contrive to cultivate a disposition--which David Hume said was better than a fortune of one thousand pounds a year--to look on the bright side of things. I think I shall, and I believe you will." The sweet-natured and great-minded man had looked on the bright side of America, and seen the good rather than the evil. He believed in our future. When Prescott died, to whom he was devotedly attached, he said: "From such a soil and in such an atmosphere, great literary men must continue to spring up."