ON THE STEENGTH OF PILLAES OF CAST lEON. 
859 
General BemarJcs on the following Experiments. 
The experiments forming the basis of this research are on the strength of cast-iron 
pillars in two series, the fii’st being on Low Moor Iron, No. 2, each 10 feet long, varying 
in diameter from 2^ to 4 inches, solid and hollow ; of these there are fourteen, including 
two on Blaenavon iron. No. 3 ; the second series are on solid pillars of cast iron, 10 feet 
long and 2^ inches diameter, from various parts of the kingdom, making twenty-four 
pillars, with two of a smaller diameter ; other pillars cut out of the preceding ones, and 
made 7 feet 6 inches, 6 feet 3 inches, 5 feet, &c. long, amount with the former ones to 
seventy- two. 
The experiments on these are distributed in Tables I. to VI. In two other Tables 
(VII. and VIII.) other experiments are given, to determine the transverse strengths of 
some of the irons, in order to compare these with their direct strength as pillars, besides 
numerous experiments to obtain the crushing strengths of the pillars, and the compara- 
tive hardness of the irons in different parts of theu’ sections. The forms of the fractures 
of pillars in the first six Tables are given in Plate XXXIII. 
It has been seen that the strength of long pillars of cast iron varies as a constant 
power n of the diameter nearly; the pillars being sohd and uniform in texture, and 
nearly as the difference of the same powers of the external and internal diameters, when 
the pillars are hollow; or as d/" in solid pillars, and D"— 6^™ in hollow ones, D and d 
being the external and internal diameters. This power n was found in my former 
researches* to be 3*56, from the mean result of many experiments on the strength of 
pillars flat at the ends. In the following experiments, which are on pillars of a larger 
kind than before, and the iron therefore somewhat softer than iron cast in smaller 
masses, the average value of n is much more near to 3’50 than to 3-55, the mean from 
nineteen comparisons being 3'513 (page 865). The strength of pillars, whose diameter 
is the same, varied inversely as the I' 7th power of the length nearly, according to the 
average result from pillars with rounded ends and with flat ends, in my former experi- 
ments. But in the present ones, on flat-ended pillars only, the power of the length 
from the results of twenty-five comparisons (page 866) is 1'63 nearly, instead of 1-7, as 
before found. 
The preceding results apply only to pillars whose length is thirty times the diameter 
or upwards; for pillars shorter than this, the formula for their strength would need 
correcting by the introduction of the crushing weight of the pillar f. 
Tables of the powers above for pillars likely to occur in practice are as below. 
* Philosophical Transactions, 1840. 
t Ibid. Part II. pp. 404, 405. 
