File:The Civil engineer and architect's journal, scientific and railway gazette (1839) (20466302670).jpg

Title: The Civil engineer and architect's journal, scientific and railway gazette
Identifier: civilengineerarc04lond (find matches)
Year: 1839 (1830s)
Authors:
Subjects: Architecture; Civil engineering; Science
Publisher: London : (William Laxton)
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Northeastern University, Snell Library

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346 THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. (October, In regard to the plan here shown as tliat for a dining room, it is not proposed as one capable of being strictly followed, because it \vouId stand in need of more or less alteration in order to adapt and adjust it, so as to combine advantageously with the rest. Of course it is here presumed that there is nothing to hinder its being executed precisely as it is represented in the cut. The door near tlie sideboard is sup- posed to open into a corridor communicating with the offices, and the other from a vestibule or ante-room, as the case might be. There are four pedestals for candelabra, and there might be others in the two arches within the recesses: these, however, are not absolutely essen- tial to the design, but might be adopted or omitted according as more or less decoration should be held desirable,—a point to be regulated by the scale of embellishment fixed upon. The recesses and semi- circular ends of the room are supposed to be floored with ornamental tiles or mosaic (like the saloon of tlie Reform Club), and the square or centre part to be covered with a rich c.irpet. Or eise the whole might be carpetted, and the same kind of di^tinction be nevertheless kept up, by putting down plain carpetting of some quiet neutral tint at the ends, for the purpose of giving more importance to the middle compartment of the room, and to the two extreme ones somewhat the air of being spacious semicircular alcoves with smaller recesses within them. After all, however, the propriety of so doing would depend upon whether any corresponding sort of distinction between the several divisions of the room was observed in the design of the ceiling. .Should the situation of the room be such as to admit of the centre being lighted from above, the ceiling might then be raised by a cove, and have a lantern occupying the rest of it. In such case no side windows would be required, still the one at the end of the room might be re- tained, unless it should be preferred to make a second sideboard recess corresponding with that at the opposite end, or to have these folding doors opening from an ante-room, substituting a niche for the present door in the recess on the left hand. ( To he continued.) ON THE FORMS AND PROPORTIONS OF STEAM VESSELS. Though reluctant to call in question the opinions of so able a writer as " H. P. H." appears to be, I think he lias no autboritv for multiplv- ing the "sectional ana of the immersed parts" of a steam vessel, into the (mean) dtjjth below the surface of the water, in order to find the resistance to her motion. Doubtless this would be correct for " flood- gates," of which one surface only is exposed to the water, and the pressure is that arising from the might of the fluid ; but the case of a vessel is totally difierent, the resistance arising not from any weight of the fluid, (for the pressure on the after half of the vessel tending to push her forward, is exactly equal to the pressure on the fore part which tends to retard her,) but from a species of friction and from the inertia of the fluid. This resistance probably increases in porportion to the densily of the water, not to its depth. As the whole of the theoretical part of the article "On the Forms and Proportions of Steam Vessels," is founded on the presumption that the resistance is proportional to the section and depth, instead of section without regard to depth, as given in mathematical works, and as It will be completely erroneous if the above view is the correct one, It may be worth while for H. P. H. to reconsider the nature of the re- sistance of which he writes, and to favour the readers of the Journal with his opinions—waiting which I am, Very respectfully, Neath, lUhof^lh month, 1841. ON THE STRAIN OF BEAMS. Sir—It may be interesting to trace the effects on beams of strains acting on them in a parallel direction. In the common hand punch, lor example there is an upright beam bent at right angles at top to a convenient distance, the extremity being fitted to receive the reaction ot the plates under the punch. Here the strain on the beam is up- ward. Instances of similar downward strains, too, are familiar, as in some portable balances, in which the scales hang from the extremity of an upright standard bent forward at the upper end. Let ABC be an upright standard rising perpendicularly from the sole N C. and beut at right angles at B; let it be subjected to a force
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acting downwards in the line A N parallel toBC. Then it would appear on a general view, that the pait BC will be equally affected throughout, as the force, which let AD represent, has the same lever- age on all points of B C. But, more particularly, in estimating the action of the force on any point M, we may consider it as acting on M by the imaginary straight lever AM. The action of the force A D on M may be analysed by drawing D F perpendicular to A M ; A D =: A F and F D, the former being longitudinal pressure along A M, the latter, a lateral strain on the cross section at M by the leverage AM. Similar resolutions for other points in BC will form right angled triangles on the common base AD, and thus the locus of the vertices of these triangles is a circle described on the diameter AD, passing through point F, of course. To ascertain how the forces A F, F D, acting on the section M, affect any other section, as that at the base C, draw AC cutting the circle at E, join D E, and complete the parallelogram O E ; draw F H perpendicular to O D, cutting A E and O D at L and H. Then A F=i A L and L F, and F D = D H and H F, these four resultants all acting at point A on lever A C ; the sura of the longitudinal strains is A L -;- HD = AL + LE = AE; the lateral strains LF and F H, acting in opposite directions =FH — FL^HL= DE. Thus the resultants of the forces A F, F D, acting on the section M, are A E and E D on section C. But A E and ED are also the resultants of AD acting directly on section C. It appears, then, that the effect of the force AD on the section C is one, whether acting directly by A C, or indi- rectly by AM C. Again, the reciprocal action of the forces A E, E D, acting directly on C, upon the section M, may be had by drawing EK, Eti perpendicular to D F, AM respectively. For we then have D E =: E K and K D, and A E = A G and G E'. Then G E or F K -f K D = F D, and A G — K E or F G = A F. But A F and F D are the resultants of A D acting directly on M. Therefore, as M and C represent every two points in B C, and as the direct action of the force AD on either point is identical with its indirect action through the other point, we conclude, generally, that its action on every cross section of B C is constant, and therefore B C ought to be of equal di- mensions from bottom to top. Draw O P perpendicular to AD, then A0 = AP andPO, and DO = OP and P D, and as PO in these two quantities acts in opposite directions, we have AO and DO = A P and P D =: AD, which intimates that there is no lateral thrust on the standard, so that the cross section of BC may at once be deter- mined from the quantities A D, NC. The part AB ought to have the parabolic outline, modified when the corner B is rounded. By supposing all the forces reversed in direction, the above demon- stration will apply also to standards subjected to upward strains. I am. Sir, Pheenix Iron Works, Your obedient servant, Glasgow, 20th ^4ug. Daxiel Clark. P. S. I think it would be a great improvement to introduce symbols to express the most common terms in papers of the nature of the pre- ceding: o fi-^r circle, i ior perpendicular, Sic.

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