712 
MR. FAIRBAIRN’S EXPERIMENTAL INQUIRY 
create serious alarm, as the loss of strength is almost entirely obviated by the new pro- 
cess of riveting used in the bottom of the Britannia and Conway Tubular Bridges*; 
and it should also be observed that in timber the same injuries are sustained by 
splicing or any other method of forming the joints as are here exhibited in the rivet- 
ing of iron plates. The two processes, that of riveting (according to the method 
used in the experiments) and splicing, when intended to resist a tensile strain, must 
therefore be considered analogous, and the comparison under sueh circumstances will 
nearly follow the same law as regards a diminution of strength. 
In this section of the inquiry the results obtained from the experiments indicate a 
loss in the joints as compared with the solid plate, as the numbers 100, 70 and 
56, viz. — 
For the solid plate 100 
For the double-riveted joint 70 
For the single-riveted joint 56 
which numbers may be considered as a fair average value of the strengths of the 
different parts of vessels constructed in this manner. 
Part V. exhibits the strength of plates to resist vertical pressure from a blunt in- 
strument, which was forced through them for the purpose of ascertaining their com- 
parative powers of resistance with oak timber, placed under circumstances preeisely 
similar and subjected to the same force. The results are interesting, as the iron 
plates appear to follow a different law in their resistance to pressure to that of oak, 
the strength being as the depth or thickness of the plates in the first case, and as 
the squares of the depth in the second. The resistances are therefore in the ratio of 
1 : 12, the iron being 12 times stronger than oak. 
In Part IV. we have some curious facts illustrative of the necessity and value of ex- 
perimental research. In the earlier experiments of the inquiry it is evident, that angle 
and T iron beams or frames are not the best, as regards form, to resist a transverse 
strain. In every case they are weak, and although exceedingly useful, and in fact 
indispensable for many purposes of construction, they are nevertheless not ealculated 
to resist strain in the form of beams or girders. These defects I have endeavoured to 
obviate by the introduction of beams with double flanges formed of a body plate and 
riveted angle-irons at the top and bottom. All these latter construetions may how- 
ever be left with safety to the practical engineer -f. 
The strengths of nearly the whole of these beams have been mathematically inves- 
tigated by Mr. Tate, to whose friendship and analytical research I am indebted for 
the annexed mathematical inquiry into the different forms of the wrought-iron beams 
which have been experimented upon. To the mathematician this part of the subject 
will be the more interesting, as the utmost care has been observed in the measurements 
* See my process of chain-riveting as exhibited in the lower sides of the Britannia and Conway Tubular 
Bridges, where the injuries above enumerated are entirely obviated. 
t For a more elaborate inquiry into the strengths of wrought-iron beams, see my work on the Britannia 
and Conway Bridges. 
