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Each extremity of the tie-rodsis bolted to a kind of shoe, (represented in figs. 5 and 6,) resting upon a stone slab on the wall, into which the lower end on the iron beam abuts, (Fig. 1.)
Fig. 2, is a plan of the roof, shewing the disposition of the frame, planking and copper sheathing. In the section, Fig. 3, the longitudinal rod is seen which steadies all the ties from lateral shake.
Fig. 7, (a) shews on a larger scale the mode in which the longitudinal tie-rods (a') are united by a bolt, (Fig. 8,) having two right-hand
screws, passing through the central coupling plates of the chains, and
the eye of the suspension vertex rod. This rod being firmly attached by two bolts (b) through the beams at the vertex, any derangement whatever of the roof, either vertically or horizontally, is effectually prevented. At each end of the roof the longitudinal rods pass through the walls, to which they are firmly fixed.
Fig. 9, shews the horizontal overlaps of the copper sheathing, which are cemented with white lead, and Fig. l0, the mode in which the copper passes over the wooden battens fixed on the planks, to which only the copper is fastened by copper rivets ; a copper cap or ridge-tile lies over the whole length, to prevent the insinuation of water at the fold: it answers this purpose so effectually, that the roof was everywhere found perfectly water-tight, during the late heavy season of rain, the first it had experienced.
The Kzisipur roof was set up without the assistance of any scafi'olding from below. An experimental truss of timber supported on chains, having been previously made to shew the advantageous application of iron chains instead of tie-beams of timber to roofs of so large a span, it was converted into a platform, moveable upon wheels along the top of the walls, upon which by means of a crane fixed at one end of the frame, the iron beams and every thing else was easily and expeditiously raised and fixed ; the beams, &c., for the opposite side of the roof being passed upon wheels across the platform. The whole frame-work was put up in 20 days.
Before closing our short account of the Késipur roof, we must notice a curious optical deception, for which we are somewhat at a loss for a correct explanation. On entering the room and looking up at the roof, it strikes every beholder that the roof has somewhat sunk, and the horizontal tie-rod is about five or six inches lower in the centre than near the walls. So firmly impressed were we of this being the case, that standing at one end of the room, and holding two fiat brass rulers, overlapping one another before the eye, we could readily measure the apparent angle of the tie-rod by raising the ends of the rulers so as to coincide with the two halves of tie-rods. On mounting the
roof and looking in at the upper window of either end, the same effect was still visible, though in a diminished degree, and we were not convinced that it was a deception, until Major HUTCHINSON at our request caused an actual measurement to be made by a perpendicular wooden batten from an accurately adjusted level on the stone floor. It was then proved that there did not exist a difference of level even to the amount of a tenth of an inch. Whence arises the illusion? Is it that the eye, judging of directions by comparison with other objects, and having the numerous lines of the pent roof inclined in opposite directions to each half of the horizontal rods, is thus perplexed in its estimate? the ruler experiment is opposed to such an explanation. It may. perhaps, be owing to the effect of light from the upper windows, which frequently gives a curved appearance to wooden beams from the decrease of illumination from side to centre. If the phenomenon resemble the effect of the eyes in a portrait always looking the same whencesoever viewed, or the curves formed by spokes of a wheel passing a railing, as has been suggested, the effect should admit of a rigid explanation, and we may hope to obtain it from some one of our readers who may have time to investigate this singular deception.
Nor]-:.—The mode of calculating the strain upon the iron rods in the above account is familiar to engineers, but it may be acceptable to others (for in India every man is his own architect), to be furnished with a correct table of the strength of timbers and iron : the following extract therefore from Mr. Basl.ow’8 report on the subject to the British Association in 1833, may be acceptable. He prefaces it by a precis of the various opinions and theories hitherto formed to explain the strain and process of fracture, and strongly recommends Taar>GoLn’s Treatises on Iron and on Carpentry. There is now no longer any disagreement on the leading principles connected with the strength of materials, excepting such as arise from the imperfect nature of the materials themselves, which furnish dilierent results even in the hand of the same experimenter.
Formulae relating to the ultimate Strength of Materials in cases of Transverse
Strain. Let l, b, :1, denote the length, breadth and depth in inches in any beam, in l w the experimental breaking weight in pounds, then will W‘ = S be *1 0°11
stant quantity for the same material, and for the same manner of applying the
straining force; but this constant is different in different modes of application.
Or, making S constant in all cases for the same material, the above expression
must be prefixed by a co-eificient, according to the mode of fixing and straining. 7 1. When the beam is fixed at one end, and loaded at the other,
Z w —-—— : S b d’ 2. When fixed the same, but uniformly loaded, ~ 1 I w
—— —- ::S.
3. When supportedat both ends, and loaded in the middle,
7. Supported at the ends, and loaded at a point not in the middle, n 11: being the division of the beam at the point of application,
Some authors state the co-eflicients for cases 5 and 6 as Q and 1‘, but both theory and practice have shown these numbers to be erroneous.
By means of these formulae, and the value of S, given in the following table, the strength of any given beam, or the beam requisite to bear a given load, may be computed. This column, however, it must be remembered, gives the ultimate strength, and not more than one-third of this ought to be depended upon for any permanent construction.
Formula relating to the deflection of beams in cases Qf Transverse Strains.
Retaining the same notation, but representing the constant by E, and the deflection in inches by 8, we shall have, '
Hence again, from the column marked E in the following table, the deflection a given load will produce in any case may be computed ; or, the deflection being
fixed, the dimensions of the beam may be found. Some authors, instead of this law
substituting for w the height in inches of a column of the material, having the section of the beam for its base,'which is equal to the weight w, and this is then denominated the modulus of elasticity. It is useful in showing the relation between the weight and elasticity of dilferent materials, and is accordingly introduced into most of the printed tables.
The above formulae embrace all those cases most commonly employed in practice. There are, of course, other strains connected with this inquiry, as in the case of torsion in the axles and shafts of wheels, mills, &c. the tension of bars
measure of elasticity, deducevit immediately from the formula
in suspension bridges, and those arising from internal pressure in cylinders, as in guns, water-pipes, hydraulic presses, &c. but these fall rather under the head of the resolution of forces than that of direct strength. It may just be observed, that the equation due to the latter strain is t ( c-—n) = n R.
where t is the thickness of metal in inches, c the cohesive power in pounds of a square inch rod of the given materials, n the pressure on a square inch of the fluid in pounds, and R the interior radius of the cylinder in inches. Our column
marked C will apply to this case, but here again not more than one-third the tabular value can be depended upon in practice.
Table of the Mean Strength and Elasticity of various Materials, from the most accurate eaperiments.
[Those marked B are extracted from Captain BAKn11’S list in the 8th volume
of the Asiatic Researches, which contains a very full and valuable list of the strength of Indian woods.—En.]
In addition to the list of desiderata promulgated by the Association, on its first meeting, which we re-published in the first volume of this Journal, page
' 308, the “ Third Report,” for 1833, contains several new suggestions and inqui
ries, whence we hasten to extract such items as it may come within the power of Indian scientific men to elucidate.
In matters of scientific announcement, we are glad to perceive, that the Eng. lish Government has undertaken the expense of reducing the observations of BRADLEY, MASKELINE, and Porn), on the sun, moon, and planets, atthe suggestion of the Association. Also, that Colonel Svxns has been requested to prepare for publication his valuable statistical returns relative to the four collectorates oi‘-the Deccan, subject to the Bombay Government; while Professor Jones is to _“ endeavour io obtain permission to examine the statistical records understood to exist in great number in the archives of the India House, and to prepare an account of the nature and extent of them.” Thus there may be some chance of the Reports of Dr. _BucHA1sAN seeing the light through this unexpected channel, although the Government of India has itself declined permitting the continuance of their
publication on the nearly gratuitous terms proposed and acted on by Captain Hnunenrr for the Dinajpfir volume* !
Dnsrnnnarn on PABLE or ILLUSTRATION IN INDIA. Meteorology. 1. Experimental data for the theory of refraction. What is the law of the decrease of temperature, or of density, in ascending? How does this vary at diiferent times ? Can any means he contrived for indicating practically at diiferent times tbs modulus of variation ? Does the refractive power of air depend simply on its density, Without regard to its temperature ? Is it well established that the effects of moisture are almost insensible ? Can any rule be given for estimating the effect of the difierence of refraction in different azimuths, according to the form of the ground? When the atmospheric dispersion is considerable, what part of the spectrum is it best that astronomers should agree to observe? 2. That the Committee in India be requested to institute such observations as may throw light on the horary oscillations of the barometer near the equator. 3. That the Committee in India he requested to institute a series of observations of the thermometer during every hour of the day and night. 4. That the decrease of temperature at increasing heights in the atmosphere
should be investigated by continued observations at stated hours and known
heights. The hours of 9% A. M. and 8-} P. M., as giving nearly the mean tempera. ture of the year, are suggested for the purpose.
5. That persons travelling on mountains, or ascending in balloons, should observe the state of the thermometer, and of the dew-point hygrometer, below, in, and above the clouds, and determine how the diiferent kinds of clouds differ in these respects.
6. That the temperature of springs should be observed at different heights above the mean level of the sea, and at difierent depths below the surface of the earth, and compared with the mean temperature of the air and the ground. Detached observations on this subject will be useful, but a continued and regular series of results for each locality will be more valuable.
7. That series of comparative experiments should be made on the temperature ‘of the dew point, and the indications of the wet-bulb hygrometer, and that the theory of this instrument should be further investigated.
8. Observations on the horary oscillations of the barometer, at considerable heights above the sea. This more particularly applies to places near the equator.
9. Observations on the phenomena of wind at two stations, at considerably different elevations. The direction of the wind should be noted in degrees, beginning from the south, and proceeding by the west.
10. That observations should be made in various places with the dippingneedle, in order to reduce the horizontal to the true magnetic intensity.
11. A regular series of observations conducted in this country on the diurnal variation of the needle.
12. That measurements should he made, and the necessary data procured, to determine the question of the permanence or change of the relative level of sea and land on the coasts of Great Britain and Ireland, (or other parts of the world.) The measurements to be so executed as to furnish the means of reference in future times, not only as to the relative levels of the land and sea, but also as to waste or extension of the land.
‘I See Preface to the second volume of the Journal Asiatic Society.