Friction
2 of the 6 encyclopedias on this shelf carry an entry for Friction. Both are reproduced below, so you can see where they agree and where they differ.
American Watchmaker and Jeweler (1892)
The resistance which a moving body meets with from the surface of the body on which it moves; is caused by the unevenness of the surfaces, combined with some other causes, such as natural attraction, magnetism, etc. It varies as does the weight or pressure applied and is independent of surfaces in contact, but if the surfaces are disproportionate to the pressure, rapid abrasion will be the result, which in its turn produces uneven surfaces and tends to increase the friction. In order to prevent the abrasion of the surface a lubricant is applied, either in the shape of oil or plumbago which, spreading itself over the surfaces of the bodies, interposes a film between the two acting surfaces, and this film, especially in light bodies, has a greater retarding influence than mere friction itself. In such cases the acting surfaces are made very minute, as in balance staff pivots, etc. In these pivots the resistance arising from the lubricant is usually greater than that of the friction proper, and it gradually increases as the lubricant becomes viscid. For this reason plumbago is advocated as a lubricant in large machines, as it does not become viscid and is an excellent lubricant. It is not applicable, however, for watch or clock work. From the above it is apparent that a light bodied or thin lubricant is desirable on small bearings, such as balance pivots, while as the barrel or power is approached and larger surfaces used the lubricant should be of a heavier body, or thicker. The nearer that a revolving surface is to its center of motion the less the friction. It is therefore essential where extra surface is desired that the surfaces be increased in length, and that the diameter of a pivot be not increased for if the diameter be doubled the resistance is doubled, as the acting surface is twice the distance from the center of motion.
Collier's New Encyclopedia (1921)
the act of rubbing two bodies together, or rubbing one body on another; in physics, the resistance which any body meets with in moving over another body. No body is quite smooth; all have elevations and depressions, and when one moves over another some of the projecting points of the one are sure to enter the cavities of the other, and render movement more difficult. Friction is greater when a body, previously at rest, first begins to move. The larger and heavier the body, the greater the friction. Friction is a retarding force in nature. It gives stability to bodies which else would be easily moved. It generates heat, and is one of the chief means of developing electricity. Co-efficient of Friction for Two Surfaces. The ratio between the force required to move one of these surfaces over the other, and the pressure between the two surfaces.
What Has Changed in the Last Century
Both entries explain friction the same way: surfaces are rough, and as Collier's put it in 1921, "some of the projecting points of the one are sure to enter the cavities of the other." That interlocking picture was largely displaced from the 1930s onward by the work of Frank Philip Bowden and David Tabor, who showed that friction between metals arises chiefly from adhesion at the tiny real area of contact where asperities are pressed together and welded, which also explains why the force depends on load rather than on apparent area, the point the 1892 watchmakers' entry states as a bare rule. The field acquired a name of its own, tribology, after a 1966 British government report estimated the huge national cost of friction and wear, and since the invention of the friction force microscope in the late 1980s friction has been measured atom by atom. Graphite, the "plumbago" recommended in 1892, is still a solid lubricant, and layered materials like it are now studied for near-frictionless "superlubric" sliding.
Written for this edition, 2026.