~37. The Effect of a Loose Bearing~ is an increase of friction, and consequently a loss of energy, resulting in the wear of _one_ or _both_ surfaces in contact, according to conditions. In Fig. 12, A is a loose bearing, B a journal at rest and C the point of contact. If the journal be now turned in the direction of the arrow by the motive force, it will have a tendency to roll over a short arc of the bearing to a new point of contact, as at D, when it begins to slide; so long as the coefficient of friction is unchanged it retains this position; but approaches or retreats from the point C, as the coefficient of friction diminishes or increases, continually finding new conditions of equilibrium. The arc of contact is thus too small to withstand the pressure without abrasion of one or both surfaces. It will thus be seen that the journal, or pivot, should fit its bearing closely; but it should be borne in mind that no tendency to "bind" should be produced, the fitting being such that the wheel will turn readily with a minimum pressure. The film of oil which must be interposed between the bearing surfaces of the journal, or pivot, and its bearing, will also occupy _some_ space; and this must be remembered, particularly in the case of pivots in the escapement. ~38. The Laws of Rolling Friction~ are not as yet definitely established, because of the uncertainty of the results of experiments, as to the amount of friction due to (1) roughness of surface, (2) irregularity of form, (3) distortion under pressure. The first and second of these quantities vary inversely as the radius; and the third depends upon the character of the material composing the two surfaces in contact. It follows, then, that in such minute mechanical contrivances as are used in horology, as the motive force is in some cases very light, the horologist should endeavor to produce, where rolling friction takes place, the maximum--smoothness of surface--regularity of form--adaptation of surfaces (31.) There are many other points on which the writer would like to dwell, as engaging and disengaging friction, internal friction, etc., etc., but the scope of this paper will not permit. ~39. The Friction Of Fluids~ in horology is of grave importance. It is subject to quite different laws from those met with in the motion of solids in contact. When a fluid moves in contact with a solid the resistance to motion experienced is due to relative motion of layers of fluid moving in contact with each other. At surfaces of contact with a solid the fluid lies against the solid without appreciable relative motion; as the distance from the surface is increased by layer upon layer of the fluid, the relative velocity of the solid and the fluid becomes greater. _Fluid friction is, therefore, the friction of adjacent bodies of fluid in relative motion._