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The mechanic is often prone to regard friction only as the deadly enemy of mechanism; the monster that gnaws away at axles and bearings, consuming both machinery and power It is true that friction produces the ill effects he attributes to it, but it is none the less true that its benefits are much greater than the evils which attend its action Of course we do not mean by this that reduction of friction is not an advantage on most kinds of machinery, or that if it could be reduced to nothing in special cases,a groat gain would not be made What we assert is that the general and total abolishment of the law of friction, would be just as disastrous, and fatal to man's existence as the destruction of the law of gravity Friction wears out clothes and shoes, but that is better than being unable to walk We have all received practical illustrations of the uses of friction, when we have had our feet slip from under us on an icy sidewalk, and found ourselves seated without ceremony and with greater force than was agreeable But there are many machines that would be totally useless without friction Without it we should be unable to use belts and pulleys, screws, or friction pulleys Without it the modern locomotive could never have existed Without it the wedge, one of the most useful and simple of mechani cal appliances, would be worthless Unlike gravity or cohesion it is, however, to a certain ex" teat controllable "by means the most of which are familiar to mechanics, and it is not our purpose to say anything in this article of the substances employed to reduce friction between bearing surfaces It is a wellestablished fact that friction is proportioned to pressure, and is independent of velocity ani extent of surface To illustrate the proposition by an example : A weight of ten pounds resting upon a surface of two square inches and moving one hundred feet in a minute, would have no greater triction than the same weight resting upon one square inch of surface and moving one hundred feet in two minutes There are some circumstances which slightly influence the exactness of the proposition but it is generally correct, and may be relied upon for all practical purposes It follows that so far as form diminishes the element of pressure it may be made to diminish friction A simple illustration of this may be obtained by laying a flat weight upon an inclined planea piece of board or a book will answer for the inclined plane The greater the inclination the less will bo the pressure between the surfaces of the weight and plane, so that the weight becomes more influenced by gravity, and descends with greater rapidity, the nearer the perpendicular is approached A screw is nothing but an inclined plane wound around a cylinder, and all who are accustomed to making large and powerful jacks, know that it will not do to give them too abrupt a pitch, as otherwise they will not support their weights without turning Here we have an illustration of the way in which form may influence pressure and through it friction In a subsequent article we shall consider this truth in its relation to the construction of gearing
