尼亚加拉天文钟。

尼亚加拉天文钟。

Dr. Pohlman, in an address before the Society of Natural Science of Buffalo, on "Recent Changes in the Falls of Niagara,” said :

“ The first scientific survey of the Falls was made in 1842 by Professor James Hall, the State Geologist of New York, and all our exact knowledge dates from his maps. Professor Hall gives the height of the American Fall as 167 feet, and of the Horseshoe Fall as 158 feet, counting the elevations from the water’s edge on October 4, 1842, and he admits that this starting point can vary from 4 to 20 feet with the rise and fall of the water in the river below the falls ; width of American Falls, 600 feet, and Horseshoe, 1800 feet. The Lake Survey went over the ground again in 1875, and in those thirty-three years the southernmost point of the Horseshoe Fall had receded 160 feet, while in the brink of the American Fall differences of 40 feel were apparent. When the American Association for the Advancement of Science met here in 1886, the section of geology decided to make Niagara the problem of the session, and for that purpose ProfessoV Woodward of Washington and some of his assistants surveyed the brink of the falls again. He found an average retrocession for the whole face of the falls of about 2 1/2 feet per annum, but as the central parts of the curve, where the water is deepest, retreated faster than the edges, for the southernmost point of the Horseshoe Fall it was found that it had traveled south 275 feet since 1875, or 435 feet since 1842, or about 9 feet every year. In view of such rapid changes it seems highly probable that the older pictures of the falls, which always place the Horseshoe Fall considerably nearer than we find it to-day, are practically correct. If the rate of retrocession remains during the next 500 years as it has been for the past 45 years, the inner edge of the Horseshoe Fail will have passed to the west of Goal Island, and as the line of deepest water is near the Canadian shore, all the waters of the river will pass over the Horseshoe Fall, obliterating the American Fall entirely and transforming Goat Island into a peninsula.