308 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[September, 



Fig. 3. 



ing to B on the other side of E A, then the points B D, will evidently 

 lie between G and K, and R and H. Let C P (in Figs. 4 & 5) represent 

 the other position of the crank, and let P T be the tangent at P. First' 



suppose the forces exerted by the connecting rods in their own di- 

 rections to be equal, then it is clear (in Fig. 3) their resolved parts in 

 the tangent will he equal, since ZEBT=ZFBT. Now from 

 F 'g. 5, it will be seen, that while the crank moves from B to K and 



from K to D, the short rod makes a smaller angle with the tangent 

 llian the long one, consequently, through this arc, the short one pos- 

 sesses an advantage ; but, on the other hand, in Fig. 4, while the crank 

 moves from A to B, and by parity of reasoning, from D to A, the long 

 connecting rod makes the smaller angle. Hence, if we suppose the 

 forces exerted by the rods in their own directions to be equal, the long 

 rod is preferable, since in a whole revolution of the crank, it has the ad- 

 vantage through the arc DAB, which is > arc B K D, through which 

 the shorter one has the advantage. But the forces exerted by the 

 rods in their own directions are not equal, since if F be the force ex- 

 erted by the piston F cos P E F.the force in the direction of the long 

 rod is always greater than F cos P F C, the force in the direction of 

 the shorter one, except when P coincides with A or K, when they are 

 equal, aud thus the superiority of the long rod in the entire orbit in 

 the transmission of rotary force, has been satisfactorily demonstrated. 

 Lastly, since the resolved part which produces rotation is greater in 

 the long than the short rod, the resolved part perpendicular to this 

 direction, or tending to the centre of the fly, is less in the long thin 

 the short rod ; and this resolved part produces friction on the axis of 

 the fly, which is the chief thing to be guarded against. 



// 18 this trifling advantage possessed by the short rod that has induced 

 several clever practical mechanics, with whom we are acquainted, to 

 argue in favour of Us Superiority ; but, whilst we agree with them, that 

 it has the properly of pressing at a more favourable angle during the 

 progress of the crank through a very s?nall arc, they must not forget the 



gradual increase and decrease of the force exerted by the piston on either 

 side of the dead power point i?,t the inequality of the forces in their own 

 directions, and that, moreover, this alleged superiority lasts only during 

 a very limited portion of the crank's entire revolution. 



Theoretically speaking then, there is no limit to the length of the 

 connecting rod of a steam engine, but in practice, we are generally 

 confined for space in the erection of machinery; still from the pro- 

 ceding analysis, we should endeavour to make it as long as we con- 

 veniently can, in order to obtain the greatest amount of rotatory force, 

 and thus render friction as little as possible. This subject might be 

 practically illustrated, by taking a steam cylinder, furnished with the 

 usual appendages, and connecting the piston rod end to the crank 

 with a rod fitted with a long eye or slot, so that the length of the 

 rod could be adjusted at pleasure. On the crank shaft put a small 

 drum, and suspend a heavy weight, that has to be wound up over it. 

 By comparing the work done in a given time with the same amount 

 of steam from the boiler, (at an equal pressure in either case,) it will 

 be found that the result of the experiment, if accurately performed, 

 will fully attest the superiority of the long rod, as shown in our theo- 

 retical deductions. 



THE BRITISH MUSEUM. 



New events produce new institutions. In the beginning of this 

 century it would have been considered a silly freak of the swinish 

 herd to have required the inspection of any architectural design, their 

 functions being limited to mute and confiding admiration, when the 

 doctors had given their fiat that the plaster palace or warehouse 

 church was a master-piece of art. What did the public know of art, 

 and what right had they to interfere? Would they have been 

 allowed to pass their comments on the lath and plaster palace in 

 Buckingham swamp? Certainly not! Neither did architects in those 

 days consider it necessary to pay deference to the judgment of the 

 public or of any one else. It was quite enough that they were em- 

 ployed to do the job, and they put it out of the way in the quietest 

 manner that they could, received the money, and posterity will neither 

 care for the architect nor edifice. The increasing attention paid to 

 English art under the auspices of George III. and George IV. led to 

 the regeneration of public feeling with regard to art, and to those efforts 

 which have been made of late years for the cultivation of the public 

 taste ; and as the public have obtained a higher qualification, so they 

 have necessarily required the exercise of higher powers. The throw- 

 ing open of the British Museum, the extension of the school in it, and 

 the establishment of the National Gallery, have opened the way, 

 which has been followed up by subsequent measures, and it is no ex- 

 aggeration now to say, that the public have twenty times the power 

 of artistic instruction which they had twenty years ago. The me- 

 chanics' institutions have co-operated in this movement by the 

 formation of drawiug classes ; and the delivery of lectures on art, the 

 extension of provincial exhibitions, or the establishment of art-unions, 

 have fostered the public disposition on the subject. Neither has the 

 government less co-operated; the improvements effected at Hampton 

 Court, the better administration of public collections, the institution 

 of schools of design, and the introduction of drawing as a branch of 

 primary instruction, have all had the same tendency. Contempo- 

 raneously a demand has been made on public grounds, on those autho- 

 rities having charge of new constructions, that the designs should be 

 submitted to public competition and public inspection, and the prin- 

 ciple of responsibility to the public voice in the case of architectural 

 works has been fully established. Acted upon by the government with 

 respect to that glorious monument, the New Palace of the Houses of 

 Parliament at Westminster, that principle has beeu carried out in a 

 most satisfactory manner in the exhibition of the Cartoons, for the 



t The circumstance of the piston's motion not being uniform is also in 

 our favour, since the force exerted varies from zero to a maximum, as the 

 piston travels from K to G and from K to H ; and whilst this fact renders 

 the advantage spoken of still more trifling, we have the long rod exercising 

 the superiority at a time when the piston's exertion is a maximum. 



