THE ELEMENTS OK MECHANISM T. M. COODEVE, M. A. HARRIS THE PRINCIPLES OF MECHANICS ETC. NEW IMPRESSION LONGMANS, GREEN, AND CO, 39 PATERNOSTER ROW, LONDON NEW YORK, BOMBAY, AND CALCUTTA 1912 All rights reserved CONTENTS. CHAPTER t PAGE I. INTRODUCTORY i II. ON THE CONVERSION OF CIRCULAR INTO RECIPROCATING MOTION 42 III. ON LINKWORK no IV. ON THE CONVERSION OF RECIPROCATING INTO CIRCULAR MOTION 148 V. ON THE TEETH OF WHEELS 168 VI. ON THE USE OF WHEELS IN TRAINS 190 VII. AGGREGATE MOTION 215 VIII. ON TRUTH OF SURFACE AND THE POWER OF MEASUREMENT 266 IX. MISCELLANEOUS CONTRIVANCES . . . . . . 284 APPENDIX 341 INDEX . . . . . 355 INDEX TO APPENDIX . 360 ELEMENTS OF MECHANISM. CHAPTER I. INTRODUCTORY. A MACHINE is an assemblage of moving parts, constructed for the purpose of transmitting motion or force, and of modifying, in various ways, the motion or force so transmitted. In order to form a definite idea of the meaning which attaches to the word machine it may be useful to refer to an example commonly met with such as an ordinary sewing machine. The apparatus is rightly called a machine, as being capable of doing work of one definite kind, under the simple condition that some natural source of energy shall bear upon it and set the working parts in motion. Upon looking into its construction we should find a fixed framework supporting combinations of movable parts, whereof some are employed in actuating a needle and shuttle, while others carry forward the material which is to be stitched. The movable parts are constrained to take certain definite motions, which are arranged beforehand, while some natural force, such as the power of the hand or the foot, is applied to the proper recipient, and then the machine does work as a necessary consequence of the action of the motive power. In commencing the systematic study of machinery, it will be readily understood that certain simple relations of motion are traceable between the prime mover which starts the machinery 2 Elements of Mechanism. and the pieces which execute the work and it is also clear that, in practice, relations governing the transmission of force must exist as certainly as those which govern the transmission of motion. The considerations relating to force may often occupy the mind of the mechanic in a greater degree than those which refer to motion but in reducing the subject to analysis it will be found convenient to separate the two points of view, and to confine our attention in the first instance mainly to Theoretical Mechanism that is, to an examination of the various contrivances and arrangements of parts in machinery whereby motion is set up or modified and to disregard or postpone any enquiry into the mechanical laws which control the forces concerned in these movements. But as the present work is intended for use and study by practical men, the author will to a small extent break through this general rule, and will take occasion, where the enquiry would be useful, of pointing out also the manner in which certain pieces of mechanism have served a compound object in transmitting exact and definite amounts of motion, while dealing at the same time with refined and subtle distinctions as to the method of transmitting force. We have now to consider and arrange the method according to which our inquiries are to be carried on, and if we were to pause for a moment and look back upon that rapid creation of machinery which followed so closely upon the splendid invention of the steam engine by Watt, we should naturally expect that some uniform arrangement for applying steam power would be adopted by common consent, and that this arrangement would powerfully influence the art of constructive mechanism...
