INTRODUCTION. 9 



arrangements ; and in the same manner we may be able, in taking- a gene- 

 ral view of other arts and manufactures, to explain their principles, where 

 theory is concerned, and to exhibit practical precedents, where the nature 

 of the subject requires no refined investigation. 



The modification of motion and force includes its communication and 

 alteration, by joints of various kinds, by wheel work, and by cordage, and 

 its equalisation by means of timekeepers. The subject of wheelwork gives 

 considerable scope for mathematical research, and requires the more notice, 

 as it has often been inaccurately treated : the consideration of cordage leads 

 us to that of union by twisting and by intermixture of fibres ; including 

 the important arts of carding, combing, spinning, ropemaking, weaving, 

 fulling, felting, and papermaking ; which constitute the employment of 

 many millions of manufacturers of all ages and sexes, in every part of the 

 world, and by which the animal and vegetable productions of a large por- 

 tion of the surface of the globe are made to contribute, as well to the power 

 and riches of the individuals who supply them, as to the health and comfort 

 of the public that consumes them. The admirable art of the watch and 

 clock maker is a peculiarly interesting department of practical mechanics ; 

 it affords employment for mathematical investigation, for experimental 

 inquiry, and for ingenious invention ; and the perfection which it has 

 derived from a combination of these means, does honour as well to the 

 nations who have encouraged it as to the individuals who -have been en- 

 gaged in it. 



To counteract the powers of gravitation and of friction, is the object of 

 such machines as are used for raising and removing weights : cranes, fric- 

 tion wheels, and carriages of all kinds, are referable to this head, and some 

 of them have been the subjects of much speculation and experiment. 

 Lastly, to overcome and to modify the corpuscular forces of cohesion and 

 repulsion, and to change the external forms of bodies, is the object of ma- 

 chinery intended for compression, extension, penetration, attrition, tritura- 

 tion, agitation, and demolition. For these purposes we employ presses, 

 forges, rolling, stamping, coining, and milling machines ; the processes of 

 digging, ploughing, and many other agricultural arts ; boring, mining, 

 grinding, polishing, and turning ; mills of various kinds, threshing mills, 

 corn mills, oil mills, and powder mills ; besides the chemical agents con- 

 cerned in blasting rocks, and in the operations of artillery. All these arts 

 are comprehended in the department of mechanics, which constitutes the 

 first division of this course. Not that we shall be able to enter at large faito 

 the detail of each ; but having formed a general outline, we may fill up its 

 particular parts with more or less minuteness, as we may find more or less 

 matter of importance to insert in each ; and those who wish to pursue the 

 subjects further, will every where be able to derive great assistance from 

 the authors whose works will be mentioned. 



The doctrines of hydrodynamics relate to the motions and affections of 

 fluids, in which we no longer consider each distinct particle that is capable 

 of separate motion, but where we attend to the effect of an infinite number 

 of particles, constituting a liquid or aeriform aggregate. The general 

 theory of such motions will be premised, under the heads hydrostatics, or 



