ON THE STRENGTH OF PILLARS. 
417 
the castings were good, and were, as before remarked, frequently bored within and 
turned on the outside, to ensure uniformity as much as possible. 
The values of b, c, and y, are calculated and inserted in the Table. I will extract 
from it the real and calculated breaking weights, that the reader may see how far 
they agree. 
Real breaking weight. 
Calculated breaking 
weight. 
Difference in parts of 
real breaking weight. 
33679 
32331 
1 
24-9 
32867 
31790 
1 
30'5 
35302 
36501 
+ — 
1 29*4 
31195 
28764 
^ 1 
12*8 
30383 
30291 
_ 1 
33*0 
41751 
40128 
1 
257 
27135 
29449 
+ — 
1 1172 
25511 
26191 
+ _L 
~ 37-5 
25105 
26273 
+ — 
r 21-49 
26729 
27364 
+ — 
' 42*0 
27135 
30863 
+ — 
~ 7-27 
37285 
40257 
+ — 
1 12*2 
34037 
31750 
1 
14*8 
Power of Cast-iron Pillars to resist long-continued Pressure. 
53. In all the previous experiments, the pillars were broken without any regard to 
time, and an experiment seldom lasted longer than from one to three hours. There 
might, therefore, be considerable doubt upon the minds of many persons whether the 
results obtained would be consistent with those which would arise from long-con- 
tinued pressure. 
At my suggestion, therefore, Mr. Fairbairn had the apparatus (fig. 2. Plate XIV.) 
erected, by which pillars might be permanently loaded. Four pillars from the same 
model were used ; they were each placed vertically upon a horizontal iron plate on 
the ground, and pressed upon at the top by means of a pin, kept vertical by passing 
through an iron collar surrounding a hole bored in the horizontal timber at the top 
of the frame. The bottom ends of these pins were slightly concave, that they might 
press, without slipping, upon the top of the pillars, which were rounded at the ends, 
whilst the top of the pin was rounded, that it might be acted upon uniformly by the 
square flat plate which rested upon it, and which by means of the suspending rods at 
the corners supported the weight. 
mdcccxl. 3 H 
