the term application has been selected as a proper one to distinguish machines that expend and apply power, from those that are employed in generating or transmitting power. machines of application employed in manufacturing, and which expend their action on material, are directed to certain operations which are usually spoken of as processes, such as cutting, compressing, grinding, separating, and disintegrating.

by classifying these processes, it will be seen that there is in all but a few functions to be performed by machines, and that they all act upon a few general principles. engineering tools employed in fitting are, for example, all directed to the process of cutting. planing machines, lathes, drilling machines, and shaping machines are all cutting machines, acting upon the same general plan—that of a cleaving wedge propelled in straight or curved lines.

cutting, as a process in converting material, includes the force to propel cutting edges, means to guide and control their action, and mechanism to sustain and adjust the material acted upon. in cutting with hand tools, the operator performs the two functions of propelling and guiding the tools with his hands; but in what [58] is called power operations, machines are made to perform these functions. in nearly all processes machines have supplanted hand labour, and it may be noticed in the history and development of machine tools that much has been lost in too closely imitating hand operations when machines were first applied. to be profitable, machines must either employ more force, guide tools with more accuracy, or move them at greater speed, than is attainable by hand. increased speed may, although more seldom, be an object in the employment of machinery, as well as the guidance of implements or increased force in propelling them. the hands of workmen are not only limited as to the power that may be exerted, and unable to guide tools with accuracy, but are also limited to a slow rate of movement, so that machines can be employed with great advantage in many operations where neither the force nor guidance of tools are wanting.

there is nothing more interesting, or at the same time more useful, in the study of mechanics, than to analyse the action of cutting machines or other machinery of application, and to ascertain in examples that come under notice whether the main object of a machine is increased force, more accurate guidance, or greater speed than is attainable by hand operations. cutting machines as explained may be directed to either of these objects singly, or to all of them together, or these objects may vary in their relative importance in different operations; but in all cases where machines are profitably employed, their action can be traced to one or more of the functions named.

to follow this matter further. it will be found in such machines as are directed mainly to augmenting force or increasing the amount of power that may be applied in any operation, such as sawing wood or stone, the effect produced when compared to hand labour is nearly as the difference in the amount of power applied; and the saving that such machines effect is generally in the same proportion. a machine that can expend ten horse-power in performing a certain kind of work, will save ten times as much as a machine directed to the same purpose expending but one horse-power; this of course applies to machines for the performance of the coarser kinds of work, and employed to supplant mere physical effort. in other machines of application, such as are directed mainly to guidance, or speed of action, such as sewing machines, dove-tailing machines, gear-cutting machines, and so on, there is no relation whatever between the increased [59] effect that may be produced and the amount of power expended.

the difference between hand and machine operations, and the labour-saving effect of machines, will be farther spoken of in another place; the subject is alluded to here, only to enable the reader to more fully distinguish between machinery of transmission and machinery of application. machinery of application, directed to what has been termed compression processes, such as steam hammers, drops, presses, rolling mills, and so on, act upon material that is naturally soft and ductile, or when it is softened by heat, as in the case of forging.

in compression processes no material is cut away as in cutting or grinding, the mass being forced into shape by dies or forms that give the required configuration. the action of compressing machines may be either intermittent, as in the case of rolling mills; percussive, as in steam hammers, where a great force acts throughout a limited distance; or gradual and sustained, as in press forging. machines of application, for abrading or grinding, are constantly coming more into use; their main purpose being to cut or shape material too hard to be acted upon by compression or by cutting processes. it follows that the necessity for machines of this kind is in proportion to the amount of hard material which enters into manufactures; in metal work the employment of hardened steel and iron is rapidly increasing, and as a result, grinding machines have now a place among the standard machine tools of a fitting shop.

grinding, no doubt, if traced to the principles that lie at the bottom, is nothing more than a cutting process, in which the edges employed are harder than any material that can be made into cutters, the edges firmly supported by being imbedded into a mass as the particles of sand are in grindstones, or the particles of emery in emery wheels.

separating machines, such as bolts and screens, which may be called a class, require no explanation. the employment of magnetic machines to separate iron and brass filings or shop waste, may be noted as a recent improvement of some importance.

disintegrating machines, such as are employed for pulverising various substances, grinding grain or pulp, separating fibrous material, and so on, are, with some exceptions, simple enough to be readily understood. one of these exceptions is the rotary "disintegrators," recently introduced, about the action of which some diversity of opinion exists. the effect produced is certainly [60] abrasive wear, the result of the pieces or particles striking one against another, or against the revolving beaters and casing. the novelty of the process is in the augmented effect produced by a high velocity, or, in other words, the rapidity of the blows.

(1.) name five machines as types of those employed in the general processes of converting material.—(2.) name some machines, the object of which is to augment force—one to attain speed—one directed to the guidance of tools.—(3.) what is the difference between the hot and cold treatment of iron as to processes—as to dimensions?— (4.)