APPLIED MECHANICS. 



[ELEOTRO-HAOMETIO ENGINES. 



practical application, that we do not think it necessary 

 to occupy space by separately discussing them. 



& By far the most important apwioattm of neat 1 

 produce motive power, is that which is made in the 

 iteam-engine. Of all apparatus by which man has suc- 

 ceeded in rendering natural forces serviceable to himself, 

 this is, perhaps, the most ingenious, as it is the incwit 

 widely employed. It therefore forms a branch of Appue 

 Mechanics, so important, and at the same time so exten- 

 sive, that we propose to devote considerable space in 

 what follows to its discussion. 



Bwtricity and magnetism are the forces which have 

 been applied no successfully in the electric telegraph an 

 apparatus which has now attained so great importance, 

 and embraces so many ingenious contrivances, that it 

 has been thought advisable to give it special consideration 

 in another section. (SECTION IV .) 



The efforts which have, from time to time, been made 

 to render these forces available as prime movers of 

 machinery, have not yet been crowned with success. We 

 may. therefore, in a practical work like the present, 

 dismiss the contrivances for this purpose with a few- 

 brief remarks as to their general character, referring the 

 reader to those parts of this work which treat more espe- 

 cially of electro-magnetism, and of the machinery ui which 

 it has been applied. 



One of the effects of electrical action being to decom- 

 pose bodies subjected to its influence in one way, and to 

 reproduce them from their elements in another way, an 

 engine was contrived to act by the alternate decomposi- 

 tion of water into its elements the elastic gases, oxygen 

 and hydrogen and its recomposition by their combus- 

 tion. The one operation, decomposition, changing the 

 small bulk of water into a large volume of the mixed 

 gaaes, afforded a pressure ; while the converse operation 



of recomposition removed the pressure by ro-cond< . 

 the large volume of the gases to the small bulk of water. 



Tho implication of eleotro-magnettsm as a prime mover 

 has been attempted in various ways, all of which dmnd 

 more or less on two special properties, by which 1 1 

 city and magnetism appear to be connected. One of 

 these is, that a current of electricity moving at rigM 

 ancles to a bar of iron renders it magnetic, each end of 

 the bar becoming a pole. When the current is reversed 

 in direction, the poles are immediately reversed, that 

 which was South becoming North, and conversely ; and 

 when the current ceases, the magnetism disappears. By 

 ooilin" the electric-wire many times round the bar, the 

 power of the magnet is rendered very great ; and as by 

 reversing or arresting the current each end may be made 

 to attract, repel, or to become entirely neutral it might 

 be expected that the force so developed should 

 readilv applicable to the production of motive power. 

 It has been found, however, that the attractive and 

 repulsive influences act with extremely little force at 

 distance from the poles of the magnet, and the conse- 

 quent limitation of range has rendered their application 

 to machinery very difficult. 



The other property by which electricity and magneto 

 are connected is, that a conducting wire wound round 

 a permanent magnet, has a current of electricity in- 

 duced in it, and the cells of an electrical battery sur- 

 rounding a magnet are put in rotation round it as 

 axis The motion produced by the mutual action of these 

 forces has not, so far as we know, been as yet applied to 

 any useful purpose ; and, although many neat contrivances 

 of the kind have been exhibited on the lecture-table, we 

 fear that in practice the cost of producing power m this 

 manner, is such as to prevent it from coming into com- 

 petition with the simple combustion of fuel 



CHAPTER V. 

 THE STEAM-ENGINE. 



POWER OF HEAT ELASTICITY OP QASE TEMPERATURE AND PRESSURE VOLUME OF STEAM 



BOILER-CORNISH BoiLER-MAn.NB AND LOCOMOTIVE BOILERS -CONSTRUC- 



BOlLER FITTINGS-FEED-SAFKTY VALVE-PRESSURE -^"'">"- 

 AND PISTON-SHUT-OFIT AND THROTTLE VALVES-FEED-rUMP-CRANK AND C 



NECTI-0 - CAMS-OOVERNOR-DIRBCT-ACTING ENGINES-VERTICAL, HORIZONTAL, LOCOMOTIVE, 



AND OSCILLATING ESOINES ESTIMATION OF POWER INDICATOR CALCULATION OF POWER. 



IT is usual for writers on the steam-engine to give an out- 

 line of its history, tracing up from the earliest times, 

 successive contrivances and suggestions for rendering the 

 elasticity of vapours applicable as a motive power. This 

 mode of introducing the student to the consideration of 

 the mechanical arrangements, which now constitute a 

 complete steam-engine, is not without its advantages. 

 It is calculated to open his mind to the defects of suc- 

 cessive inventions, and to the modes in which they have 

 been gradually removed, until what was at one time 

 looked on as an ingenious and interesting philosophical 

 toy has become at last an apparatus that has changed 

 the'whole face of civilised society, and almost brought 

 the elements within the control of man. By watching 

 the steps of inventors in this progress, the student 

 becomes well prepared to comprehend the details of the 

 perfected apparatus, and tho reasons why certain modifi- 

 cations have been introduced as improvements, while 

 rs have been rejected as practically inapplicable. 

 But it happens with the steam-engine as with almost all 

 other mechanical contrivances, that its earliest forms are 

 by no means the most simple ; and that improvements 

 have often consisted more in discarding useless com- 

 plications than in adding new parts. Wo think, upon 

 the whole, therefore, that the steam-engine may bo best 

 studied in rU most rimplo forms, regardless of their 

 historical sequence, especially when a practical know- 

 ledge f iU construction and applications is desired, 

 rather than a merely theoretical acquaintance with its 

 principles. We propose, therefore, to discuss, in the 

 first f lace, tho general properties of steam, and the 



modes adopted for generating it in a manner suitable for 

 rendering it available as a prime mover. And we will, 

 secondly, consider tho special forms of apparatus, or 

 engines, through which the steam is made to act for 

 producing the movement of machinery. By this course 

 we shall hope to give the reader a clear view of tho 

 whole subject ; and wo shall take such opportunities as 

 offer themselves, of referring to tho various inventions 

 that have, from time to time, been brought into use. 



To the advantages arising from the use of steam as a 

 motive power, to the changes that have been effected by 

 its introduction, and tho still greater changes that may 

 be confidently expected from its more extended applioa- 

 tion, we need scarcely refer. These are patent to all ; 

 for in the present condition of society, few operations 

 either of transit or manufacture are conducted, in which 

 tho steam-engine does not play the most prominent 

 part. 



EXPANSIVE POWER OF HEAT. When V liquid 

 is exposed to heat, it expands in bulk ; and when the 

 heat is carried to a certain point, part of the liquid rises 

 from tho rest in the form of vapour, occupying a much 

 greater volume than it did in its liquid condition. It is 

 probable that all substances, solid as well as liquid, are 

 r;i]iable of being thus changed into tho vaporous form. 

 Some bodies, such as ether and alcohol among liquids, 

 and iodine among solids, rise in vapour at comparatively 

 low temperatures. Others, again, such as many of tho 

 metals, even after they have become liquid under the, 

 influence of heat, require very considerable accessions of 

 temperature before they pass into vapour. Water, one 



