There is nothing in the heavens, nor in the earth, that proves to us positively that the sun holds the planets, and the planets their satellites, by attraction, as we are taught that the moon attracts the water of our world. We see that all terrestrial bodies tend toward the center of the earth, and we call this gravitation; but we cannot see how a body moves around the earth without falling on it, by this law. We say in dynamic philosophy, that bodies move in the direction of least resistance, and _that_ we can positively understand; but what force _per se_ is, we do not know. It is always better for us to explain phenomena by positive known laws and motions, than by any that rest merely upon conjecture. Lancaster, Pa. JNO. WISE. * * * * * The Great Hoosac Tunnel. Messrs. Editors:--In No. 23, Vol. XVII., of your paper, is an article upon the Hoosac Tunnel, but made up from data nearly a year old, and consequently not correctly representing the tunnel as it is at the present time. Your conclusions of course were based upon the same data; but during the past year, and especially during the past five months, much greater progress has been made than ever before upon the work, and a knowledge of what has been done since the last report was issued will, I think, give you a different impression of the time required for its final completion. Referring to the profile in that number of the SCIENTIFIC AMERICAN, the following are the distances to the various points where the work is being prosecuted: Distance from east end to central shaft 12,837.294 feet " " central shaft to west shaft 9,747.072 " " " west shaft to new shaft 265.000 " " " new shaft to well No. 4 659.150 " " " well No. 4 to pier[1] 1,522.825 " ---------- " " east end to pier[1] 25,031.341 " [Footnote 1: The instrument pier is 4 feet west of the present west end of the tunnel.] The following are the lengths of the headings at the various points of the work, Dec. 2, 1867: Length of east end heading 4,608.000 feet " " west shaft, east heading 1,262.000 " " " " " west heading 611.000 " " " west end heading 617.000 " ---------- Total length of headings 7,098.000 " Leaving 17,933.341 " or 3,396 miles of heading yet to be made, of which 1,218.975 feet are between the west end and the west shaft, and 16,714.366 feet between the west shaft and east end of the tunnel. The central shaft is down 583 feet, and well No. 4 is down 150 feet. The progress for the month of November, 1867, was as follows: