STATICS AM) DYKAMTCS.] 



APPLIED MECHANICS. 



779 



useful pursuit without that aid. Practical Mechanics 

 may indeed be called the handmaid of the other arts. 

 The sculptor, the architect, the musician, the chemist, 

 the astronomer, the surgeon, the merchant, the manu- 

 facturer, the builder, the military man, the civilian, the 

 traveller, and the emigrant, all require her services all 

 reap the benefit of her labours. 



It is generally supposed that inventors in the arts, aa 

 well as discoverers in the sciences, owe their success to 

 some fortunate accident. We tliink it may, in most 

 cases, be shown that such is not the fact. Almost every 

 famous discovery, or useful invention, has been the re- 

 sult of long, often painful and laborious, thought and 

 research ; and success has often followed repeated failures ; 

 accuracy has succeeded repeated errors. That, there is a 

 natural genius for invention peculiar to some minds, 

 cannot be doubted ; but that genius alone, without 

 labour and study, has ever led to brilliant results, may 

 as (irmly be denied. Mechanics, as an art, in a peculiar 

 manner demands concentrated thought ; there should be 

 no waiting for some inspiration to bridge over a me- 

 chanical difficulty. Let a man gird himself to his task, 

 and determine thoroughly to think out the subject he 

 may have on hand, and we venture to predict that he 

 will find few difficulties insurmountable. 



MECHANICS AND CHEMISTRY. The two sci- 

 ences that deal with matter in its various affections and 

 modifications are Chemical and Mechanical Philosophy. 

 The former treats of the influences affecting its minute 

 par cles, and the combination of these particles; the 

 hitter has reference to masses of matter, and the forces and 

 motions of masses, or aggregations of particles. Each of 

 these two sciences frequently encroaches upon the other's 

 domain, for there are many similar phenomena developed 

 by the action of natural laws on masses as well as on 

 particles, and thus it is often difficult to draw a line of 

 separation between the subjects of the two sciences. 

 Questions relating to heat, light, electricity, and mag- 

 netism, form part of both sciences alike, and can scarcely 

 be said to belong to the one more than to the other. 

 There are questions, however, which are purely chemical, 

 and others as distinctly mechanical. 



The chemist, examining a piece of matter, tries its 

 specific gravity, its solubility or fusibility ; analyses it, 

 and finds the different elementary substances which 

 compose it, and the precise quantities in which they are 

 combined. 



The practical mechanic, examining a structure or a 

 machine, sees, feels, and measures the parts of which it 

 consists, traces the laws that govern its equilibrium or 

 its movements, and determines the principles which have 

 been adopted in its construction. 



STATICAL AND DYNAMICAL MECHANICS. 

 The objects of Practical Mechanics may be divided into 

 Statical and Dynamical. Statical mechanics has refer- 

 ence to the formation and arrangement of materials 

 intended to remain in a state of rest ; its principal 

 objects are permanence and stability. It has to consider 

 the strength, elasticity, flexure, weight, and durability 

 of the materials with which it deals. It has to employ 

 the proper substances for its purposes, put them in their 

 right places, make them of suitable forms, and unite 

 them firmly together, or so arrange them, that the ten- 

 dency to change their relative position when affected by 

 external forces shall be the least possible. The civil and 

 the naval architect, or the builder, whose business it is 

 to make large fabrics by putting together numerous 

 small pieces, is indebted for the durability and strength 

 of his structure to the application of statical mechanics. 

 So, also, the miner or the civil and military engineer, 

 who has to form extensive excavations, erect embank- 

 ments, bridges, tide-works, or fortifications, requires, an 

 intimate knowledge of statical mechanics. 



Dynamical mechanics, on the other hand, has reference 

 to the forms and combinations of materials with a view 

 to motion. Its principal objects are the generation, 

 communication, and application of power and force, in 

 order to change the forms or arrangements of materials. 

 Its products are tools, implements, machines, engines, or 



apparatus ; it teaches us how to choose the most suitable 

 ( materials, produce the strongest and most serviceable 

 forms, arrange their respective motions so as to secure 

 regularity and diminish resistance, with a view to 

 i economy of labour and durability of structure. The 

 farmer, brickmaker, and stone-worker, the carpenter and 

 the smith, the spinner and weaver, the worker in pottery 

 ; and metals, are all employed in changing the forms and 

 arrangement of the materials submitted to them ; and 

 they have all to use the apparatus provided by the ma- 

 chinist, and the machinist practises the art of dynamical 

 mechanics in devising and executing the implements 

 suitable for their and his own use. 



In statical and dynamical mechanics, the chief study 

 is economy of material, labour, and cost. In any struc- 

 ture, whether for stability or movement, by an un- 

 sparing use of materials, it may generally be possible to 

 secure the necessary strength. But it frequently happens 

 that the usefulness of a construction would be seriously 

 diminished by a rude accession of mere strength ; and, 

 in all cases, elegance of construction is manifested by the 

 careful and ingenious arrangement of materials, and not 

 by their absolute mass. Accordingly, we find, that as 

 mechanical art advances, lightness and neatness of struc- 

 ture take the place of magnitude and weight ; and im- 

 provements in existing constructions or arrangements 

 are made to depend for their merits on the saving of 

 material and labour which they effect. Perhaps the 

 most stable structures that mankind have ever formed 

 are the pyramids ; and as works of enormous magnitude, 

 of great age, and mysterious purpose, they excite admira- 

 tion and wonder. But when one considers their form 

 and the arrangement of their parts, their durability is 

 not to be wondered at. A hill of mere sand, not blown 

 upon by strong winds or washed by heavy rains, would 

 retain for ever its pyramidal form, and would be an 

 object of as great beauty and utility as the pyramid it- 

 self. The sovereigns of Egypt had probably at their 

 command an enormous amount of human powor, and 

 knew no better object on which to employ it, than the 

 erection of some immense pile, to gratify their pride 

 while living, and contain their bodies when dead. We, 

 living thousands of years after them, do not see the 

 pain and labour of their slaves, and scarcely know how 

 much misery might have been spared mankind, had their 

 labour been applied to better uses. In the mere paving 

 of the metropolis, we have more material and labour 

 applied to a useful purpose than the amount required for 

 the largest of the pyramids. In our harbours and docks, 

 our canals and railways, we have works far more stupen- 

 dous ; and in our steam vessels and manufactories, we 

 have power at work exceeding the capabilities of the 

 whole ancient world. But with all this, it is the object 

 of the engineer and machinist to study the greatest pos- 

 sible economy of material and of labour. 



STRENGTH OF MATERIALS. Whatever be the 

 elements which constitute beauty, in works intended for 

 ornament, we see beauty in things made for use, just in 

 proportion to their fitness for their purpose. Parts out 

 of place, deficiency or redundance of material, elaboration 

 not called for, and deviation from just proportion, be- 

 come glaring defects in any structure or apparatus formed 

 for useful purposes ; and no amount of decoration or 

 finish can reconcile us to a disproportioned or unskilfully 

 designed fabric. It is, therefore, most important that the 

 practical mechanic should form an intimate acquaintance 

 with the strength of the various materials with which he 

 deals ; their powers to resist strains in various directions, 

 and the arrangements suitable for making use of these 

 qualities to the greatest advantage. In the theoretical 

 portion of this subject, there is much that is abstract and 

 mathematical, yet nothing so difficult, but that the fair 

 exercise of judgment may lead to very sound conclusions 

 respecting it. All the main facts, however, respecting 

 the strength of materials, are the result of experiment 

 and observation ; and the true use of theory in a subject 

 like this, is to analyse and classify these results. If it 

 be found, for instance, that several beams of timber, of 

 known dimensions, are capable of sustaining certain 



