SECOND REPORT - 1882. 
612 
of 4 feet asunder, and broken by a weight at the middle; one 
with the rib upwards, to compress it, and the other with the 
rib downwards to tear it asunder. The former required nearly 
four times as much to break it as the latter. 
These experiments show clearly the serious consequences 
which might result from turning iron beams, of the usual form, 
wrong side up, as is frequently done in factories ;—though, ac¬ 
cording to the theory which ascribes equal resisting powers to 
tension and compression from equal forces in this material, the 
beams ought to hear the same weight turned either way. 
To apply the views developed by these experiments, and by 
theory, to beams of cast iron, the author sought to obtain — 1st, 
By a series of experiments, the form of a beam which would 
bear the most without breaking;—2nd, The variation in strength 
arising from changes in the dimensions of such beam;—3rd, A 
practical rule for the measure of its strength at the time of 
fracture. 
With respect to the general form of the cross section, in the 
middle of the beam, that was assumed to be the best which has 
a strong rib at top and bottom, with a thin solid sheet between 
them; the strengths of the ribs and sheet being in proportion 
to the strains upon them. The best proportion of this form at 
which the author -was able to arrive, was one in which the bot¬ 
tom rib was more than two thirds of the whole section; and, 
from a comparison of all the experiments, it appears that in 
those beams which approach to the best, the strength is nearly 
in proportion to the size of the bottom rib in the middle, the 
length and depth of the beam being invariable. 
The great size of the bottom rib, in this form, rendered it 
desirable to reduce it towards the ends of the beam. This was 
done by making the bottom rib parabolic, and the beam of equal 
height throughout : so formed it was uniform in strength, made 
a level floor, and afforded the greatest saving of metal. 
A number of experiments were next made to ascertain the 
effect of a variation in the depth only of these beams, every 
other dimension being constant. These were made on beams 
of considerable size, some of them being 9 feet between the 
supports, and upwards of 10 inches deep. The result from 
these experiments was—that the strength was very nearly as 
the depth. 
From the above two properties, then, we derive for the ulti¬ 
mate strength of cast iron beams of the best form, the following 
General Hide . —Multiply the area of a section of the bottom 
rib, in the middle, by the depth of the beam, and by a constant 
quantity, and divide thi's product by the length. 
