1842.J 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



» 



benefit in Ptnulating the consprvators of the ship of Colchis, who ac- 

 complisihed repair after repair until not a vestige remained of the 

 original stnioture. 



The definitions at the commencement of (he volume, showing the 

 precise acceptationof the terms wheel and pinion, trundle or wallower, 

 teeth, cog, leaves and staves, are suitable enough, but we cannot see 

 the utility of inserting in a work like the one before us, simple geo- 

 metrical definitions, which may be found in several professional edu- 

 cational elementary works, besides about 20 pages filled with tables 

 of square and cube roots. Surely the roost moderate penetration might 

 have discovered such insertions as these to be not merely superfluous, 

 but to constitute a sort of "caput mortuum," highly detrimental to the 

 quality of the work. Without conferring the smallest degree of benefit 

 they create prolixity, induce confusion, and increase the expense of 



I the book, at the same time that they diminish its value. Having said 

 thus much on the superfluous part of the work, we shall now proceed 

 I to direct the attention of our readers to the more valuable portions. 

 i The following remarks (page 192) are judicious. 



I " Nor perhaps doe-i the timptieitt) of a machine consist strictly in having 

 , few moving partt. if the part^ of a machine be few, they arc perhaps more 

 easily taken in by the eye at one view, which may make them morr eaiily 

 comprehended hy the mind, and in that sense )>c more simple. But in ma- 

 chinery the kind of simpUcity at which we ought to aim has more regard to 

 the nMnjie^ qf action than to the number of moving parti." 



I In page 95, we have a very useful table of the proportions of wheels 

 I in actual use, which we very willingly insert here. 



TABLE OF PITCHES OF WHEELS IN ACTCAL USE IN IIILLWORK. 



Kind of Machine. 



Water-wheel ■ , A 



Water-wheel-, B 



Water-wheel, C 



Water- wheeP, D 



Horse-mill, E 



Horse-mill, F 



Steam Engine, by B. & W. G. 

 Steam Engine, by B & W. H. 

 Steam Engine, by B. & W. I. 

 Steam Engine, by B. & W. K. 



Steam Engine, L 



Ditto, ditto*, M 



Ditto, rlitto', N 



Ditto, ditto", 



Ditto, ditto, P 



Ditto, ditto', Q 



Ditto, ditto, R 



1 Has b'.^n 16 years at work. Teeth much worn. r . , , • ■ 



2 Ua^ been 16 years at work. This geanng was found rather loo narrow for the strain, as it is wearing much faster than the rest ol the wheels m the 



3 Tlie only defect in this Rearing, which has been IC years at work, is the want of breadth in the spur-ttheel and pinion : they ought to have been 6 



inches or more, as they will not last half so long as the bevel-wheels and pinions connected with them. 



4 This is a tieiter pilch for the power than Q. 



5 ilii» wheel has wooden teeth, and has been working for three years past. 



6 Ditto. 



7 This pitch has been found to be too fine. 



EXPLANATION OP THE TABLE OP WHEELS IN ACTUAL I'SE IN HILLWOBK. 



The wheels are all reduced to what may be called one denomination. 



First — Dy proportioning their breadths all to what they should be to have 

 the same strength, if the resistances were equal to the work of a steam en- 

 gine of ten horses' power. 



Second — By supposing their pitch lines all brought to the same velocity 

 of three feet per second, and proportioning their breadths accordingly. I 

 have chosen this particular velocity of 3 feet per second, because it is the 

 Telocity very common for overshot water wheels. 



Such cases as appear to have worn loo rapidly, are marked, which may 

 tend to discover the hmit in point of breadth. 



The Appendix A on the teeth of wheels by Professor Willis, is an 

 important and well written paper, already known to the public, through 

 the Reports of the Proceedings of the British Association, at the meet- 

 ing held ut Newcastle, and the Transactions of the Institution of Civil 

 Engineers. The leading feature of this piiper is the development of 

 a method of making any pinion to work correctly with any wheel of 

 the same pilch. 'Tlie following extract explains the manner in which 

 this is accomi>lishcd. 



" From among the infinity of cnrvei that may be oifered the epicycloids 

 and involutes have been universally prefencd, on account of the facility with 

 which they can be merhanieally denoribed, and perhaps because Ihcy admit 

 of ready and independent dcuionitrations of their poticising the properties 



required. But the practice has liitherto been confined to that class of epicy- 

 cloids which work correctly with straight hnes or circles. Teeth formed 

 upon these principles possess this inconvenience, awheel of a given pilch and 

 number of teeth, say 10 if it be made to work correctly with a wheel of 50 

 teeth of the same pilch, will not work correctly with awheel of 100 teeth of the 

 same pitch. This is obvious, for the diameter of the describing circle by which 

 the epicycloid is formed must be made equal to the ra.lius of the pilch circle 

 of the wheel with «hich the teeth are to work, and will therefore be twice 

 as large in the second case as in the tir»l. 



In the old style of niillwork in which the teeth of wheels always consisted 

 of wooden cogs, this property offered no very serious im|>eiliinenl, although 

 as we shall sec it introduced some complication of method ; but in the mo- 

 dern practice of making cast iron wheels the objection is a very serious one. 

 A founder must make a new pattern of a wlieel of 40 teeth for every com- 

 binalion thai it may be required to make uf this wheel with olliers, and the 

 same for a wheel of any other number. Besides, it often hap|)cns in ma- 

 chinery that one wlieel is required to drive two or more, whose number of 

 teeth arc dilTirenl, and in this case the teeth cannot be correctly formed at all 

 on the common principles ; ond again the |ierfeclion of machinery is impaired 

 from the temptation to employ in one combination patterns which have tieeii 

 formed for another combination very nearly the same, for example, Io make 

 a wheel of 40 teeth Ihal has been formed to work with one of 811, serve fur a 

 reipiired combination of 41) «illi 85. 



" It is essentiul llicrefurc that the teeth of wheels should if possible be •« 

 formed as to allow a given wheel to work correctly with any other wheel of 



