INTRODUCTION*. H 



the purposes for which they are employed, we shall separately examine the 

 principal machines and manufactures in which those forces are applied to the 

 service of mankind. 



Such instruments and machines as are more or less immediately suhservient 

 to mathematical purposes, will be the first in order, including- all the meclian- 

 ism of literature, the arts of writing, engraving, and- printing, in their various 

 branches, and the comparison of measures, with each other and with differ- 

 ent standards ; the principles of perspective will also form a useful appendage 

 to the description of geometrical instruments. The determination of weights, 

 and of the magnitude of moving forces of various kinds, constituting the sci- 

 ence of statics, will be the next subject, and will be followed by the con- 

 sideration of the retarding force of friction, and of the passive strength of 

 the various materials, that are employed in building and in machinery. 



All these subjects are in part preparatory to the immediate examination of 

 the mechanical arts and manufactures, which are so numerous and complicated 

 as not to admit of regular arrangement without some difficulty: they may 

 however be divided into such as are principally employed for resisting, for 

 modifying, or for counteracting, any motion or force ; thus architecture and 

 carpentry are chiefly intended to resist the force of gravitation : these compre- 

 hend the employments of the mason, the bricklayer, the joiner, the cabinet 

 maker, and the locksmith. In these departments it is often of the utmost im- 

 portance to the mechanic, to recur, especially in works of magnitude, to philoso- 

 phical principles ; and in many other cases, where there is no need of much 

 calculation, we may still be of service, by collecting such inventions of in- 

 genious artists, as are convenient and elegant, and which, although simple in 

 their principles, are not obvious in their arrangements; and in the same man- 

 ner we may be able, in taking a general 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 alter- 

 ation, by joints of various kinds, by wheelwork, and by cordage, and its 

 equalisation by means of timekeepers. The subject of wheehvork gives con- 

 siderable scope for mathematical research, and requires the more notice, as it 



