398 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



Deo. 



fB9ade, sent to Ihe Inslitute by Cavaliere Niccolo JIatas. The dome is 

 one of the earliest modern domes, and second iu size only to St. Peter's, at 

 Rome, but older. 



Some discuasioD took place on Ihe propriety of Ihe raeeling coming to 

 an otf-hand vote, approving of the design of Cavaliere Matas, and at length 

 a commillee was appointed to examine and report. 



ON MODEL EXPERIMENTS. 

 (Continued from page 3i3.J 

 la the last number of the Journal we obtained formula for the compari- 

 son of the weights capable of being sustained by similar girders; we now 

 proceed to apply our foriuu!;e to the experiments so ably conducted by Mr. 

 Hodgkinson, with reference to the proposed bridge over the Menai Straits. 

 A report of these experiments will be found iu the May number of the 

 Journal for 18-iG, from which we extract the following table and explana- 

 tion : — 



"To obtain the strength of tubes, precisely similar to other tubes fixed 

 on, — but proportionately less than the former in all their dimensions, as 

 length, brcaiUh, depth, and thickness, — in order to enable us to reason as to 

 strength from one size to another, with more certainty than hitherto, as 

 mentioned before. Another object, not far pursued, was to seek for the 

 proper proportion of metal in the top and bottom of the tube. Much more 

 is required in this direction. 



In the three series of experiments made, the tubes were rectangular, and 

 the dimensions and other values are given below. 



The tube placed first in each series, is intended to be proportional in every 

 leading dimension, as distance between supports, breadth, depth, and thickl 

 ness of metal, and any variations, are allowed for in the computation. Thus 

 the three first tubes of each series are intended to be similar ; and in the 

 same manner of the other tubes, &c." 



Here it will be observed that in the first set the dimensions are four times 

 the dimensions in the second set nearly, and the dimensions in the second 

 set are very nearly twice those in the first. Comparing the first of the 

 second and third sets, we find in the first of the second set the weight of 

 the tube 78 lb. 13 oz., and the breaking weight 9,976 lb. ; and in the first of 

 the third set, the weight of the tube 10 lb. 12 oz., aud the breaking weight 

 2,4G4 lb. Now, by the formula deduced in our last paper, if w be the im- 

 posed breaking weight, w' the weight of a girder in scale 1, the breaking 



weight of a similar girder in scale u will be ( _ '""("— ) '" \ ^„^ 

 Here (a-l) = l ; w' = 10 lb. 12 oz. ; w = 21b.; i(; = 2,464 lb. ; 



2v;- («-l) w' --- 4918 lb. nearly 



2!0 — {u—\)w' 



«= = 983G. 



This, as will be seen, is only 140 lb. less than the breaking weight as found 

 by experiment. It will he observed, moreover, that the tube in the second 

 set is rather more than twice as thick as that in the fiist, which sufliciently 

 accounts for the slight discrepancy. Comparing now the first experiment of 

 the first and second sets, we shall find the value of the breaking weight in 

 the first, deduced by the formula from the second— too great : 



putting M = 41b., M)' = 78 lb. 13 oz., «j = 9,9761b., 

 the breaking weight were = 70 tons,— an excess over experiment of nearly 

 13 tons. The reason of this dill'erence is obivous : our formula supposes 

 that the breaking tension per square inch, in all the models compared by it, 

 is constant. This, no doubt, would have been the case in the model tubes 

 of Mr. Hodgkinson, had they been constructed of one uniform plate of 

 metal, and not rivetted. The necessity of rivetting is one great cause of the 

 mishaps which are constantly occurring in iron briilges,— as we endeavoured 



to show a few numbers back, in a paper on the cause of the breakage of the 

 Dee Uridge [see Journal, p. 204] : the longer the bridge, the wider and 

 more numerous must be the joints, and the greater the chance of irregular 

 strains. The effect of rivetting, we observe, has been to reduce the breaking 

 tension per square inch one-fifth, in the first of the first set of experiments 

 as compared with the first of the last set ;— how much that effect would be 

 increased in a tube 460 feet long, or fifteen times the dimensions of the 

 longest experimented on by Mr. Hodgkinson— we leave our readers to 

 judge. 



We trust, in the meaawhilc, that Mr. Hodgkinson will continue his labours 

 on tubes of still greater length, by which means only can we hope for any- 

 thing like an approximation to a law for the mean effect of a number of 

 rivetted joints. However, as we have often observed, the mischief most to 

 be apprehended is not of a statical but dynamical character,— the constant 

 recurrence of vibrations, tending to loosen the joints, perhaps to impair the 

 nature of the iron, and ultimately so to weaken the structure, that a shght 

 jar or strain may be sufficient to produce sudden disrupture of the whole. 



CITY OF LONDON UNION WORKHOUSE COMPETITION. 



A controversy is going on as to the competition for this building, which 

 is likely to draw the general attention of the profession. The facts we 

 are informed, are these. 



The surveyor who measured the ground for the guardians is named as 

 the favoured candidate, aud by a majority of two obtains the award of the 

 first premium. He has resorted to the extraordinary measure of sending 

 round to the guardians a plan and particulars of his own design, and so 

 has brought himself before the tribunal of the public. On this plan he is 

 charged with having taken 17 feet more ground in width than is allowed 

 to the other competitors, the presence or absence of which would make a 

 great difference in the accommodation, as the space of ground is uncom- 

 monly narrow. 



Had the matter rested merely with the board of guardians, we could not 

 have interfered until a decision had been given ; but as Ihe surveyor has 

 pleaded to the jurisdiction of the public, we feel that we have a full right 

 to institute such a comparison between his and the second plan, as will 

 show that there are no sufficient reasons for the selection ; and under the 

 peculiar relation of the surveyor aud the board of guardians, we cannot 

 but look with suspicion on the present state of the case. 



The comparison, unfortunately, is of the defects of the surveyor's plan, 

 from which the other is free. Only eight day rooms are provided for 

 1,000 inmales,— but then the surveyor says that two " work rooms" are 

 day rooms, and two "dietary rooms" in the basement are day rooms, hav- 

 ing, consequently, two sunk areas as airing yards. No separation is made 

 of aged women, mothers with children, and prostitutes, who are to be 

 placed in one day room. The rooms for aged couples are made to look out 

 on a dead wall close by, and having privies and urinals beneath. The 

 infirmary does not contain sufficient accommodation. The Poor-Law Com- 

 missioners have wisely protested against dormitories on the ground-floor, 

 but the surveyor has provided them. The passages are circuitous^ and 

 many of them will require gas in the daytime. 



As the strip of ground is long and narrow, the surveyor has made his 

 buildings to stretch across it, so that they can be built against at a future 

 time, and light and air excluded. 



As to the design of the chapel which he has sent round, we cannot but 

 think it too ornate and preposterous as applied in such a building. 



The other plan runs in one compact block along the ground in its great- 

 est length, ha\iug wide spaces on each side for courts and yards, which 

 can never be interfered with by any buildings on either side. One corridor 

 is carried through the building from end to end, proper access is provided, 

 fourteen day rooms are laid down, no communication can take place be- 

 tween the sexes, and even the male and female infirmaries are separated. 



A body of masters of unions have pronounced in favour of the second 

 plan and against that of Ihe surveyor, and it is certain that the latler will 

 be rejected by the Poor-Law Commissioners. Whether Ihe board of 

 guardians, who are friends to the surveyor, will dare to pass his plan after 

 llie discussion whicli has taken place, remains to be seen ; but if they do, 

 we shall cerlainly not fail in our endeavours to do justice to the architec- 

 tural profession. 



