THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



204 



Tredgold's theory of the stcan. en;;inc bears the sr.me relation to the truth 

 v,bich the speculations of the old (ireek philosophers respect.ng planetary 

 motion bore. The evaporative power of the boiler as an ,ngred>ent of nu- 

 : al calcula.ion is e'ntirely neglected in Tred^old's theory, and the gross 

 Trrors of principle with which his work is mied are made ten t.mes wo .e 

 bv Mr. Woolhouse's profession of having corrected the,,,. It .s really too 

 late, now that De Parabour's masterly investigations have been for s,. or 

 .even years before the world, to endeavour to revive Tredgold s exploded 

 views and we regret that the trealise before us should have been .n- 

 j„red by this injudicious attempt. However the reader is, we are very 

 Mad to find, put upon his guard in the preface, and it is therefore h>s own 



''r;.r^^m:nr:;'i,e present work is the vast quantity of inh^rmation 

 whicl. it alfords as to details of construction. In this respect ■' f-ms un- 

 nvalled. The only thing to be complained of under .h,s head >s that a 

 large amount of matter is frequently compressed into so small con, pas. that 

 he eader will often have a difliculty in finding the informat.on for wh.ch 

 he s in search. The book is not sufficiently digested-not systemat.c 

 enoug It contains avast store „f invaluable facts, but these l.keoter 

 warehoused commodities, are frequently so crowded together that U .s d.f- 

 hcult to get at them. Mr. Bourne talks of having a new ed,t,on we hope 

 ,1 a he n ay be encouraged ,o do so, and that he will adopt >n U a s.mp le 

 lid Let arrangement by vU.ich the reader may find " every th.ng >u .ts 

 place, and a place for every thing." 



[JULT, 



Hand Book of Mapping and Engineering Drawing. By B. P. 'W iI-ME. 

 London: Weale, 1846, quarto. Parte. Page 6i). 



This is the concluding part of a practical treatise on engineer.ng draw- 

 i„g, which has been already favourably noticed by us. The P-^n part 

 contains a comparison of the different methods of copy.ng maps « descr.p- 

 tl of drawing instruments, methods of representing geological strata, &c. 

 There are some useful suggestions respecting the execution of Parliamentary 

 Plans, which will be of interest to some of our readers, and may be quoted 

 as a fair specimen of the character of the book. 



" By the standing orders of the House of Commons, engineers and snr- 

 vevorsVre required to plot their railway plans at a scale of no le^s than 

 veyors are icquii ."p,,, ^,,:j,i, of railway surveys vanes from 5 to 20 



20 chams to an inch, fhe width ot f^' J ■ j^,, ,■„( ,„ i,, ^,. 



ft' Uo s^:' Tef IV ir e plot; nnd number all honsls, fields, &c., 

 tended to '%*^° .^■'^^;"2lil,„' rhe limits of deviation are certain lines 



vvnen ran ^jy pnlareed plans of those subdivisions of land 



usual C<=°"P" f° 'y '° f !" '" dX ,P„„ses, &c., subdivisions being often 



tXVesXl ho.h by drawing and numbering ; a -P-^ ^-^f^ -'f 



J "id'JLf be written, an'd of late days the co«„/, -- -^P -^me ^f 



Inn of each sheet. The sheets are numbered 1,2, 3, iit., ana tne name oi 



he hue of railway is sometimes written over the number o the street as 



Elvertou No 1. The enlarged plan should be p aced in each case direcUy 



tumbled together that H '^^l^i^-if j-;:;-^ 7 1 1^ in ^'::^ 

 It: c"reVo°cc;: ; t tt ^lu i-i-- «' a scale of 20 chains to an 

 rncMtee'aUrged plans are usurUy plotted at a scale of five chains to an 



'"The scale of si. chains to an inch is one frequently adopted (or F^vli^- 



.1^ frradw.y pi^ ; ^f^^^^^^ :^^:z:.'::z:^n^ 



mmmmm 



^r^ca;:: Tins is done with a ;>- . ..bscure a. - - P-^^> 



ad«,iS of plans being drawn at a large scale it ''/f '^^^^ ';'" "^^ "' 

 the time be sbojt, the work will be sooner done at a small scdlt. 



« \gain for the duplicate plans ; this becomes a consideration. Litho- 

 Eraphers charge a less sum for lithographing and printing plans at a small 

 ^cale, than at a large one. Lithography has of late years become a very 

 favourite medium with engineers and surveyors, for the production of dup- 

 licate plans for parliamentary deposit. It certainly has much to recom- 

 mend it, and in proper hands, it would he a most invaluable medium. It 

 is to be regretted tliat this art, (as applied to the purpose above named), 

 almost essential to the surveyor, has fallen into the hands of an ignorant 

 class of persons, viz., the picture-copiers and lithographic printers. It 

 were impossible to detail the mischief annually done by persons being in- 

 trusted with this class of business, who are totally ignorant of the construc- 

 tion or use of maps. The numerous railway schemes brought before I ar- 

 liament during the last two sessions have compelled engineers and other 

 persons intrusted with the getting up of plans and sections to employ a 

 miscellaneous collection of persons, who had never before been similarly 

 enaaaed A proportionate amount of mischief has been the consequence. 

 It is painful to see even the professed picture-copiers or lithographic artists 

 attempt to copy plans. The most ridiculous blunders are made, as nnght 

 be expected : but of this no more. The remedy is simple ; at least the evil 

 may lo a great extent, be le5sened,if not altogether removed. Letsurveyors 

 lithograph their own plans, or employ their draughtsmen upon them ■ much 

 tine and expense would thus be saved. The picture-copiers and litho- 

 ..raphic artists would no longer have their brains addled with pursuits 

 ^bove their capacity ; and the lithographic p'inters would have the plans 

 put into their hands in a perfect state, instead of being oh iged o send 

 them back to the lithographic ignoramus for every alterauon of his blunders 

 required to be made by the engineer, on examining proofs. In fact, by tb« 

 method recommended above, the necessity of proving may be m a great 

 measure dispensed with. i i „■ • . 



"The principal point to be attended to in getting op such drawings is to 

 draw them accurately. There is seldom time for pains-taking with em- 

 bellishment, and the plainest style of execution is quite as useful as the 

 most elaborately finished production." 



The work is illustrated by excellent plates, and seems to convey detailed 

 information on every point connected with the execution of architectural 

 and engineering drawings. 



THEORY OF THE STRENGTH OF M.VTERIALS. 



In our last number we published a paper on this subject, by oar old 

 correspondent Mr. Byrne, and as some of the arguments on which his 

 viewsare founded, seem insufficient, we do not hesitate, iiot«ithstanding 

 our respect for Mr. Byrne's scientific attainments, to state where his opinion 

 differs from our own. 



The new theory proposed seems to be founded on the idea that there 

 does not exist in deflected beams what is termed a neutral line. Now it 

 appears to us that the existence of this line is capable of being proved by 

 several methods which possess the strictness of mathematical demonslra- 

 tion Before however, detailing these proofs, it may be as well to define 

 what is meant by a neutral line, and to reply tp the argument brought to 



disprove its existence. j „ . , i • . i 



The originators of the term " neutral line" stated that when a honzoDtal 

 beam supports a transverse weight, the upper part of the beam exerts a 

 thrust and the lower part a tension, and since these two portions of the 

 beam exert opposite kinds of action, there must be in the beatn sonie in- 

 termediate part which marks the transition from one state to the other- 

 where therefore, there is neither thrust nor tension. They asserled more- 

 over that the actual position of this neutral line, or rather neutral boundary, 

 depended on the dimensions of the beam, the degree of deflection and the 

 wei-ht supported ; and their theory has hitherto been considered incontro- 

 vertible Mr Byrne however brings forward this argument against ,t- 

 he savs'that if a beam be deflected and a slice be taken in the upper part 

 fit(fi- 3 P 164). ""is slice has the same form as the whole beam, and 

 consequently there is as much reason for assigning a neutral line to the 

 slice as to the whole beam. The consequent inference would be that the 

 beam has an infinite number of neutral lines, but this absurdity is to be 

 deduced, not from the original theory, but merely from Mr. Byrne s method 

 of stUing it. For when he says that the/orm of the thin upper slice is an 

 argument for the existence of a neutral line in it, he makes the neutral ,ne 

 depend merely on the form of the beam and not on its mechanical action 

 an t ,e connection of Us parts. If the slice a were actually cut off and 

 ' parated from the retuainder A, so as to have no connection with it then 

 whe bent ,t would no doubt have a neutral line of its own. And if ben^ 

 Ts represented in the figure, while lying upon A, the lower side o a would 

 Tot le "omuch extende^d as the upper side of A, but there would be some 

 such difference as that in the diagram. 



