The next communication was by Mr. SEARS C. WALKER, through Prof. ALEXANDER ON THE OPPOSITION OF NEPTUNE OF 1848. Mr. SEARS C. WALKER communicated to the Section the comparison of his Ephemeris of Neptune, for the opposition of 1848, with the observations received from Hamburg and Cambridge, England. After applying to the Ephemeris a correction published by Mr. W. in the American Journal of Science, the differences between the computed and observed places of Neptune, are as follows: This comparison shows that no correction is needed as yet, either to Mr. Walker's elements of Neptune's orbit, or to the perturbations of the planet, as computed by Prof. PEIRCE. The following paper was read: ON THE TOPOGRAPHY OF THE STATES OF PENNSYLVANIA AND OHIO, &c. BY SOLOMON W. ROBERTS, Esq. The speaker commenced by saying, that the maps which he exhibited, showed the results of numerous and extensive surveys, which had recently been made. A rail-road is in use from Philadelphia to Harrisburg, on the Susquehanna, a distance of 107 miles, passing over a rolling and highly cultivated country, but not crossing any high ridges. The Pennsylvania Rail-road, now in course of construction, from Harrisburg to Pittsburg, at the head of the Ohio river, will be 251 miles in length, making the whole distance from Philadelphia to Pittsburg, 358 miles. This line crosses the Alleghany mountain at Sugar Run Gap; and from Harrisburg to the base of the mountain, a distance of 133 miles, the line follows the valley of the Juniata river, and has no grade greater than 21 feet per mile. The curvatures are easy, and the road adapted to high velocities. The mountain is ascended on the eastern side by 12 miles of a grade of 80 feet per mile, similar to that on the Western Rail-road of Massachusetts. The summit of the mountain is then passed by a tunnel 700 yards long, and the line from the summit to Pittsburg is 106 miles long, with a maximum grade of 52 feet per mile. The rail-road distance from Pittsburg to Cincinnati will be 330 miles, by the way of Massillon, Wooster, and Columbus, while the distance by the Ohio river is 495 miles, or one half longer than the rail-road; and the rail-road may be traversed in about one-fourth of the time required by steamboats on the river. The rail-road in Ohio for the greater part of its length will traverse the elevated table lands of that state, which are very favourable for rail-road construction. The speaker described the principal topographical features of the States of Pennsylvania and Ohio, and exhibited a profile of the crest line of the Alleghany mountain for a distance of 44 miles. In conclusion, he explained that the best and shortest rail-road route from Cincinnati to New York and Boston, passed through Pennsylvania and Philadelphia; and that the same was true of a road from St. Louis. And also that from Cleveland on Lake Erie to New York, the distance by the rail-road through Pittsburg and Philadelphia, will be 80 miles shorter than by the way of Dunkirk and Piermont. A communication was read on DEFINITIONS AND DISCRIMINATIONS RESPECTING MATTER, VOID SPACE, AND NIHILITY. BY PROF. ROBERT HARE. In what respect does a void space resemble nihility? In what do they differ? Space can hold either matter or spirit, nihility neither. Nothing can hold nothing. Space implies the capacity to hold something, whether corporeal or spiritual, and differs from nihility as a mathematical solid differs from a mathematical point. It is unity in imagination, multiplied three times by any number representing imaginary length, breadth, and thickness, whence results an imaginary solid. How does space differ from matter? Matter is capable of any degree of motion, space utterly immovable. Yet to move matter requires a force, and to stop it when in motion, force is requisite. The ability to retain its actual state, whether of rest or motion, has been designated as the power of indolence, "vis inertiæ," and the consequent motive force when in motion, as momentum. Of the vis inertiæ, either as constituting momentum, or resisting it, space is, of itself, as destitute and insusceptible as nihility. The most minute portion of matter avails as something; the largest portion of space is, per se, equivalent to nothing. Agreeably to Newton, the atoms of matter are bodies endowed with inertia and gravitation, and each occupying, exclusively, a commensurate portion of space, must have the cohesion necessary to perfect hardness or impenetrability. ence. According to Faraday and others, it is only necessary to suppose atoms to consist of certain forces acting from their respective centres. But if the supposed centres be mathematical points, they must emanate from nothing, since, physically, a mathematical point has no existOut of nothing, nothing can come. Besides, one mathematical point being precisely similar to any other mathematical point, any forces emanating from any one such point, must equally belong to all such other points; and since mathematical points must be infinite, both as to number and as to ubiquity, the universe would be a plenum of inseparable and undistinguishable forces, instead of those which actually exist as appertaining to the various parts of space, casually and transiently occupied by what we call matter. But if, instead of assuming the centres of forces to be ideal mathematical points, it be supposed that the centre of each force is concentric with a minute globular space, which it casually occupies, evidently the globule thus suggested, must have essential attributes of a material particle. It can have no association with the containing space, since space is immovable matter, susceptible of any degree of motion. That of which our planet consists, revolves about the sun with inconceivably swift motion, rendered extremely complicate by diurnal rotation, and revolutionary reaction with the moon. No matter in this planet, or in any other, can exist in the same space for more than an infinitismal of time. Hence, as neither mathematical points, nor minute spaces existing about them, can be endowed with the forces and properties usually attributed to matter, these forces and properties must belong to some thing existing about the centres whence they proceed, and within the spaces whence they act. When any space is found to be the seat of a force, it follows, inevitably, that there is a material body or bodies therein, which causes it to differ from any like space which is vacant, and of course destitute of any power. It follows, that whatever is susceptible of motion, and capable of exercising any force or reaction, is a material body according to science, as well as common sense. It follows, from the preceding reasoning, that spiritual existence involves that of kind of matter; spirits must be endowed with the power of locomotion, and cannot be confounded with mere space, any more than other bodies. The Section then adjourned. B. SILLIMAN, JR., Sec'ry. Saturday, September 23, 4 P. M. The Association met agreeably to adjournment-President, W. C. REDFIELD, in the chair. The Standing Committee reported, that it did not deem it necessary to fill the blank in the 18th rule of the Association; but that for the present year the annual subscription of one dollar, together with such voluntary subscriptions as the members may severally feel able or inclined to add, will, in all probability, be found sufficient to meet the expenses of publishing the proceedings. It was thereupon resolved, that the said blank shall for the present remain. The Standing Committee also recommended that a complete catalogue of the members of the Association be prepared by the Secretary, and that the Treasurer call upon the members to pay their annual subscriptions, together with such voluntary contributions as they may be inclined to make; which recommendation was adopted. Prof. PEIRCE having resigned his place as a member of the Standing Committee, on motion of Prof. W. B. ROGERS, Lieut. MAURY was appointed to fill his place for the remainder of the session. On motion, Resolved, That the Secretary of the Association be authorized to procure separate books for the minutes of the General Association, and for those of the separate Sections. On motion of SOLOMON W. ROBERTS, Esq., it was Resolved, That the Standing Committee be requested to memo rialize the Legislature of Pennsylvania, in favour of the publication by the State, of the final report of the geological survey of Pennsylvania. On motion of Lieut. MAURY, it was Resolved, That the Committee on the sediment of the Mississippi river be requested to continue their investigations, with a view of ascertaining and reporting the probable effect which the reclaiming of the drowned lands of that river would have upon the improvement of its navigation, and the health of the country in the vicinity of the drowned lands. Prof. AGASSIZ read a communication ON THE ORIGIN OF THE ACTUAL OUTLINES OF LAKE SUPERIOR. He stated, that along the entire northern shore of the lake, and for some distance inland, as well as in the islands on that side of the lake, six distinct systems of dykes are exhibited, each consisting of numerous broad parallel beds of igneous erupted matter, and that the direction of the islands and successive parts of the coast line, were seen to conform themselves to the bearing of these dykes, as presented in each part of the coast. Thus it appeared that the physical outline of the shore of the lake, was determined by the geological structure of the adjoining land. He adverted to the enormous magnitude, as well as the great number of these great igneous beds, and to the vast extent to which metamorphic phenomena are witnessed in the structures and other sedimentary matter lying adjacent to the igneous masses. In relation to the subject of Prof. AGASSIZ's communication— Prof. W. B. ROGERS remarked, that from his observations on the southern shore of Lake Superior, and from those of other observers in that region, it was apparent that the east and west dykes, lying adjacent to that margin of the lake, had in like manner determined the chief peculiarities in the configuration of the coast. He also called attention to the fact, of the remarkable correspondence between the igneous and metamorphic masses, described by Professor AGASSIZ as existing on the northern side of Lake Superior, and the great belt of the Blue Ridge in Virginia, extending from the Potomac to some distance south of the James river. The immense extent of epidotic trap, and other masses abounding in epidote, and the various mineral |