INTO THE STRENGTH OF WROUGHT-IRON PLATES. 
705 
ternal pressure increases in the ratio of the squares of its thickness ; and, where great 
strength is required, it will be necessary, in the construction of vessels, to consider 
the nature of the service and the required thickness of the planks. 
The same remarks will apply to vessels constructed of iron, computed from the 
formula deduced from the experiments. In a table of experimental results by Mr. 
Hougkinson we have the mean force per square inch required for crushing timber of 
different kinds ; and assuming Rondelet’s experiments, which give 70,000 lbs. as the 
resistance per square inch of wrought iron, to be correct, we then have as the ratio 
of their respective powers of resistance as follows : — 
Table XV. 
Specific gravities. 
Description of 
timber used. 
Resistance per 
square inch. 
Resistance of 
wrought iron per 
square inch. 
Ratio, the wood 
representing 
unity. 
7-700 
0-560 
Wrought iron 
Yellow pine 
lbs. 
3373 
lbs. 
70,000 
70,000 
1 
: 13-02 
0-340 
Cedar 
5674 
70,000 
1 
: 12-33 
0-580 
Red deal 
5748 
70,000 
1 
; 12-16 
0-640 
Birch 
6402 
70,000 
1 
: 10-93 
0-660 
Sj-camore 
7082 
70,000 
1 
: 9-88 
0-753 
Spanish mahogany ... 
8198 
70,000 
1 
: 8-53 
0-780 
Ash 
8683 
70,000 
1 
: 8-06 
0-700 
Dry English oak 
9509 
70,000 
1 
: 7-36 
0-980 
Box 
9771 
70,000 
1 
: 7-16 
In addition to the relative resisting forces of the different kinds of timber above 
enumerated, will be found the specitic gravities of each, which enables the reader to 
determine the comparative weights as well as strength of the different kinds of wood. 
PART IV. 
In the preceding researches I have endeavoured to determine the value of iron 
chiefly in reference to its application for the purposes of ship-building. It now only 
remains to determine the best form and condition of another part of the structure, 
namely, the frames and ribs of vessels, also composed of iron. Some of the forms ex- 
perimented upon indicate weakness, but certain modifications which have since been 
introduced, have given increased support to the bilge and sides of the ship, and greater 
powers of resistance to the outer sheathing. The beam shown at fig. 19, Plate LVIII., 
is probably one of the strongest and most suitable for the support of the decks, but it is 
inadmissible as a frame for receiving the exterior sheathing plates. These frames are 
generally formed of a plate with angle-irons along the edges on both sides, of which 
the annexed sketch are sections, a, a, &c. 
Fig. 
15. 
represents a portion of the outside plates : 
C 
c 
c 
^ ^ . i 
h, b the angle-iron frames or ribs, which 1 
r 
r 
r 
r 
'f 
vary from 18 to 24 inches asunder, ac- y 
if 
if 
, hj 
cording to the position in the direction 
a 
a 
4 X 
MDCCCL. 
