SECTION IX. 

 PRACTICAL OR APPLIED MECHANICS. 



CHAPTER I. 



INTRODUCTORY. 

 Contents. MECHANICS or AHTKJCITT MODERN MACHINERY MECHANICS AND CHEMISTRY STATICAL AND DYNA- 



MICAL MECHANICS STRENGTH OF MATERIALS - POWER STANDARD OF POWER SOURCES OF FOWER APPLICA- 

 TION OF POWEK FRICTION GOVERNING POWER NATURE OF MACHINES MECHANICAL EDUCATION. 



PRACTICAL MF.CIIAXICS is the art of applying the theo- 

 retical principles of mechanical philosophy to materials, 

 so that they may be fashioned, arranged, and combined 

 in the various forms required by man. It is difficult in 

 any case to draw an exact line of separation between the 

 theoretical aiid the practical : for all true theory is 

 founded on practice, and all skilful practice is the appli- 

 cation of true theory. In the case of Mechanics, the 

 separating line between the theory and the practice is 

 eminently difficult to be traced ; for the development of 

 principles depends at every step upon practical experi- 

 ment, and the improvements in mechanical arts are 

 generally the results of extended research into the prin- 

 ciples. It is true, indeed, that a great range of mecha- 

 nical theory can be investigated by abstract reasoning 

 upon a few simple principles, just as mathematical science 

 is built upon a few definitions and truths ; but it is re- 

 markable that little progress was ever made in mechanical 

 science until men began to translate the actual results of 

 experiment. In Mathematics, which is certainly the 

 science of all others requiring the least amount of experi- 

 in'-iital proof, the ancients made considerable progress, 

 because the minds of men in former times were quite as 

 well fitted for the investigation of abstract truths as 

 those of modern mathematicians ; but in the sciences 

 which demand experimental proof such as Chemistry, 

 Optics, Astronomy, and Mechanics little progress was 

 ever made until philosophers began to observe facts, 

 and thence reasoned to their causes. For many ages of 

 the world's history, it was the custom-of men pretending 

 to science to start in their own minds a hypothesis or 

 conjecture about some law of nature ; to build upon this 

 slippery foundation a vast scheme of nature ; and then to 

 wonder that natural phenomena did not suit their 

 arrangement. In some such way as this the astronomers 

 of old, with a few illustrious exceptions, took it for 

 granted that an enormous, in their notions a boundless, 

 mass, such an the earth, could not move ; and, therefore, 

 that the sun, moon, planets, and stars, revolved in daily 

 cycle round it. And it was not until observations had 

 been carried on for many centuries until the records of 

 these observations had been compared and digested, and 

 until instruments had become so far perfected as to 

 enable astronomers to observe with accuracy that the 

 true theory of the celestial phenomena was developed. 



.Ml. < II ANirs OF ANTIQUITY. In respect of me- 

 chntiical science, the ancients appear to have been very 

 They had, indeed, tolerably true notions re- 

 specting the construction of buildings in such a manner 

 M to ensure permanence and stability ; but for these 

 qualities thev seem to have depended almost entirely on 

 rude strength and mamiveness, instead of skilful arrange- 

 ment. Among the gigantic remains of Egyptian archi- 

 tecture, there is not found a single arch ; the only 

 approach to it is the vault of a passage hollowed like an 

 n arch, but made of two or three immense blocks of 

 Uiuo cut to the vaulted form. Again, among the ruins 

 778 



Fig. 1. 



of Central America, remarkable for their enormous ex- 

 tent and elaborate decoration, the passages of such 

 buildings as remain tolerably ent.re are found to be 



covered by blocks of 

 stone, arranged as in 

 Fig. 1. The beautiful 

 id stable 



and stable arrange- 

 ment of materials in 

 the form of an arch 

 does not seem to have 

 occurred to the archi- 

 tects of antiquity, 

 until the compara- 

 tively recent era of 

 the Roman Empire. 

 It is difficult to ascer. 

 tain whether the an- 

 cients were acquainted with any of the forms of roofs 

 now in use, on account of the perishable nature of the 

 materials : but it is probable that they knew no such 

 method of covering large spaces ; and for covering apart- 

 ments of more limited extent, they had no resource but 

 the use of large masses of stone. 



In respect of machinery, the ancients appear to have 

 been extremely deficient, for we have records of no 

 apparatus except certain implements of war and of the 

 chase, and a few rude contrivances for irrigating and cul- 

 tivating the ground. But, indeed, even in modern times, 

 the mechanical arts had made little advance until the 

 genius of Watt had given to man a power applicable alike 

 to manipulation of the most delicate character, and to 

 labour demanding the most gigantic strength. Could a 

 man who lived in England but a hundred years ago now 

 revisit his country, he would in mechanical art find a 

 change far greater, an advance more astonishing, than 

 the whole progress made from the creation of the world 

 up to the time at which he lived. 



MODERN MACHINERY. That a man seeing all 

 the wonders of modern art, as they have been seen of 

 late years at the great Exhibitions, should endeavour to 

 attain a knowledge of their nature and construction, may 

 at first sight appear presumptuous, because of the vast 

 extent and variety of the objects which wo would have to 

 study; and, indeed, unless one were prepared to devote 

 his lifetime to mechanical art, ho could scarcely hope to 

 know accurately the details of modern machinery, niiu'h 

 less to attain the skill of a master in all its varied de- 

 partments. But, with a fair knowledge of some simple 

 first principles, and an introductory glance at a few of 

 the leading details that are common to all mechanical 

 arrangements, we believe it would not be difficult to attain 

 a good general knowledge of mechanical art, and a readi 

 ness at comprehending any mechanical arrangements that 

 may be brought under our notice. Few will be incline ! 

 to dispute the advantages of possessing even such a 

 moderate knowledge of Mechanics as this implies, for in 

 modern times but little advance can bo made in any 



