had made to the botanic garden at Cambridge a donation of nearly 4,000 very choice specimens of dried plants of central Europe, which, with the assistance of Mr. Seringe of Bern, he had collected in Switzerland. During Dr. Cogswell's active superintendency of the Astor library, he prepared a valuable alphabetical and analytical catalogue of its contents, which was published in eight large volumes, displaying his extraordinary knowledge of the history, comparative value, and significance of the books he had collected. He continued to perform the active duties of superintendent with singular industry and fidelity, until the pressure of advancing years induced him to retire in 1860. Two years later, having changed his residence to Cambridge, Mass., he resigned the office of trustee. After that time it was his habit to make annual visits of several weeks to his friends in New York. While his physical strength gradually failed, his intellectual powers remained unimpaired to the advanced age of 85, and his sparkling conversation was as interesting as in earlier years. His remains were interred in his native place, where a handsome monument is to be erected by his Round Hill pupils, to testify their affection for their old friend and instructor. He bequeathed one fourth of his moderate fortune to the Manning school of Ipswich, Mass.
COHASSET, a town of Norfolk co., Massachusetts, on the South Shore railroad, 15 m. S. E. of Boston; pop. in 1870, 2,130. It borders N. E. and E. on Massachusetts bay, and is surrounded on all other sides by Plymouth co., being separated on the west by Hingham from the main body of Norfolk co. The peninsula of Nantasket, constituting the main portion of the town of Hull, and forming the S. E. side of Boston harbor, projects N. W. from Cohasset about 5 m., and contains Nantasket beach, 4 m. in length, which is much resorted to for its beauty, fine shell fish, sea fowl, and good bathing. The coast of Cohasset is very rocky, and is noted as the site of Minot's ledge lighthouse. The Conohasset river, which anciently formed the boundary between Plymouth and Massachusetts colonies, flows through a portion of the town. In the S. W. part is a pond of 90 acres, abounding in fresh-water fish. The situation of the town is delightful and romantic, and its ready access from Boston has rendered it a popular summer resort. The inhabitants are chiefly engaged in mackerel fishing and the coasting trade. Cohasset until 1770 formed a part of Hingham, and was called Conohasset, an Indian name signifying a fishing promontory.
COHESION, that kind of attraction by which the particles of bodies are held together, as the molecules of water, of iron, or of stone. It is manifested in a high degree in solids, less in liquids, and but very little or not at all in gases. The molecules of which bodies are composed would seem, from the various phenomena observed in nature and in experiments, to be under the influence of two opposing forces, which under varying conditions alternate with each other in preponderance. One of these forces is molecular attraction, and the other is molecular repulsion. The first is exerted only at inappreciably small distances, but the laws by which it is governed are not known. Bepulsion is exerted at greater distances, and is principally controlled by the action of heat, increasing as the heat increases, the abstraction or addition of this agent being usually sufficient to cause matter to assume either the solid, liquid, or gaseous form. Molecular attraction manifests itself in three ways, by cohesion, by adhesion, and by chemical affinity. The degree of cohesion in the same solid depends much upon the arrangement of its particles, as may be observed in the different degrees of hardness between tempered and untempered steel, and the difference in tenacity of metals in ingots or in hammered or rolled plates. The distinction between cohesion and adhesion is not always easily to be established. Adhesion is commonly spoken of as existing between the particles of dissimilar bodies, but it is more accurately defined by calling it that molecular force which holds two distinct bodies together, whether they are of the same substance or not. If two pieces of lead have plane surfaces cut upon them, and these are firmly pressed together, they will continue to be so held by the force of adhesion (independently of atmospheric pressure), and not of cohesion, because that term cannot strictly be applied except when such a union has taken place as to render the structure continuous between the original bodies. To consider, also, cohesion as only capable of existing between particles of the same kind, would lead to conclusions that cannot well be maintained, because in an alloy of two or more metals, even when they are not mingled in the proportions of their atomic weights, it seems proper to consider the particles as being held together by the force of cohesion. As has been intimated, the laws which govern molecular attraction are so imperfectly understood that the relations between cohesion, adhesion, and chemical affinity cannot be stated. The last named force is exerted between atoms or molecules of matter which are not of the same kind; it is manifested with more intensity than is observed in the phenomena of cohesion and adhesion, and is also followed by a more intimate union of the particles, by which the formation of a new body, unlike in its physical properties either of those of which it is composed, is accomplished. Heat exerts a remarkable influence upon these forces, and indicates the differences which exist in their nature. Adhesion does not seem to be so uniformly diminished by its action as cohesion, for the adhesion between substances is often increased thereby, while cohesion is constantly diminished. Chemical affinity is also generally increased with the increase of heat, certainly while union is taking
