PREFACE. THIS book is divided into three parts: the first treats of the Geometry of Machinery; the second of the Dynamics of Machinery; and the third of the Materials, Strength, and Construction of Machinery. Under the head of the Geometry of Machinery, machines are considered with reference to the comparative motions only of their moving parts; and rules are given for designing and arranging those parts so as to produce any given comparative motion. Considering that the object of such rules is to adjust the dimensions of the parts of machines by processes of practical geometry, I have thought it advisable to solve every question by drawing, rather than by calculation, except in a few special cases where calculation is indispensable. Many of the graphic rules thus obtained are made more easy and accurate, and some, indeed, are made possible which were not so before, by the aid of new methods of measuring and laying off the lengths of curved lines. Two chapters of the first part are devoted to the detailed consideration of the movements of single pieces in machines. The remainder of the part relates to Pure Mechanism, as defined and reduced to a system by Professor WILLIS. The order in which the various combinations in mechanism are treated of is different from that adopted by him; but the principles are the same. Several problems in mechanism are solved by methods which, so far as I know, have not hitherto been published; and which possess advantages in point of ease or of accuracy. I may specify, in particular, the drawing of rolling curves, and of some kinds of cams; the construction of the figures of teeth of skew-bevel wheels, and of threads of gearing screws, by the help of the normal section; and some improvements in the details of processes for designing intermittent gear, link-motions, and parallel motions. Under the head of the Dynamics of Machinery are considered 171258 the forces exerted and the work done in machines; the means of measuring those quantities by indicators and dynamometers, of determining and balancing the reactions of moving masses in machines, and of regulating work and speed; and the efficiency, or proportion in which the useful work is less than the total work, in the different sorts of moving pieces, and in their various combinations. Considering that a convenient single word is wanted to denote the proportion in which the total work in a machine is greater than the useful work, I have ventured to propose the word COUNTEREFFICIENCY for that purpose. Under the head of the Materials, Strength, and Construction of Machinery are considered, first, the properties of various materials, as affecting their treatment and use in the construction of machines; secondly, the general principles of the strength of materials; thirdly, the special application of those principles to questions relating to the strength and the construction of various parts of machines; and fourthly, the principles of the action of cutting tools. Great care has been taken to ascertain the values of the factor of safety and of the working stress in successful examples of actual machinery; and some of the problems respecting the strength of special parts of machines have not been published previously except in scientific journals and in lectures. Authorities for facts and information are cited where it is necessary to do so. The following works are so frequently referred to, that it may be desirable to mention them here specially:WILLIS On Mechanism, first edition, 1841; second edition, 1870. FAIRBAIRN On Millwork. HOLTZAPFFEL On Mechanical Manipulation. BUCHANAN On Millwork; edited by TREDGOLD and G. RENNIE, with an Essay on Tools by NASMYTH. W. J. M. R. The Seventh Edition has been revised, and additional matter relating to recent improvements added to Appendix. GLASGOW, May, 1833. W. J. M. CHAPTER I.-ELEMENTARY RULES IN DESCRIPTIVE GEOMETRY. SECTION I. General Explanations: 22A. Given, the Projections of a 17. Given, the Traces of a Straight Line; to draw its Projections, 18. Given, the Projections of a 19. Given, the Projections of Two Points; to measure the distance 20. Given, the Projections of a Point, and the Projections of a Straight Line through that Point; to lay 21. Given, the Projections of a Straight it makes with one of the Planes 22. Given, the Projections of a Pair of a Plane traversing that Line; SECTION IV.-Rules Relating to Planes. 23. Given, the Projections of Three a Plane passing through them, 9 23A. Given, the Projections of Two Points and of a Straight Line; 24. Given, the Traces of a Plane; to 31. Given, the Traces of a Plane and the Projections of a Point; to and parallel to the given Plane, 13 32. Given, the Traces of a Plane, and 33. Given, the Traces of a Plane, and the Projections of a Point; to 34. Given, the Projections of a Point, which shall Traverse the Point, 35. Given, the Projections of a Point draw the Projections of a Per- 36. Given, the Projections of Two |