422 
MR. HODGKINSON’S EXPERIMENTAL RESEARCHES 
59. We have seen in the preceding abstract from Table XII., that the longest 
wrought-iron pillars of the three classes there considered, have their strengths as one, 
two, three nearly ; bat that the shorter pillars, those of 30^ inches long, or less (the 
diameter being 1-015 inch nearly), differ much less in their relative strengths. These 
in the 30^ inch pillars being 
Ends round. Ends round and flat. Ends flat. 
15480 21355 23371 
15480 21187 25387 
The second and third of these numbers in either series are much less than twice and 
three times the first number, which was a mean from three experiments. 
We see, therefore, that these second and third numbers are the results from pillars 
which were affected by some cause that did not reduce the strength of the pillars of 
equal diameter and length, which were broken by the first weight, 15480 lbs. For 
it will be seen further on, that this first weight was as great as is in accordance with 
the results from the longer pillars. 
60. To determine the cause of this anomaly, which had first been exhibited in the 
experiments upon cast iron, and afterwards was found to take place in wrought iron, 
steel, and timber, I felt to be very difficult. The experiments upon cast iron offered 
no satisfactory explanation of the matter, for it usually changes but little in form 
before fracture. Wrought iron appeared, therefore, to be a better material for ex- 
hibiting the cause. 
Three small cvlinders of the same iron as that in Table XII. were therefore formed. 
They were each exactly inches long and -62 inch diameter, their ends being turned 
flat and perpendicular to the axis ; they were subjected to compression with their 
ends well-bedded, and after bearing certain weights they were tried by a gauge which 
had exactly fitted them before. The results are in the table below. 
No. of 
Experiment. 
Weight 
laid on. 
Weight per square 
inch. 
Reduction in length. 
Remarks. 
lbs. 
lbs. tons. 
inch. 
1 
6222 
20610 = 9-2 
•o? 
No alteration, or, if any, extremely small. 
1 
7342 
24319 = 10-9 
•015 
1 
8462 
28028 = 12-5 
•02 
Diameter sensibly increased, cylinder not bent. 
2 
12444 
41218 = 18*4 
•04 
f Diameter increased from ‘62 to ‘63 inch, 
\ slightly bent. 
3 
18667 
<X> 
G4 
II 
O 
CO 
00 
0D 
•16 
Bent a little, diameter increased to ’65 inch. 
We see, from the above, that 6222 lbs. produced no sensible change in the cylinder 
*62 inch diameter, but that 7342 lbs. and 8462, particularly the latter, which was 
equal to 12| tons per square inch, produced very obvious changes. 
Since the resistance to crushing are as the areas, the former of these two values 
would give 19677lhs., and the latter 22679 lbs., for the pressures which would pro- 
duce an equal alteration in a bolt 1’015 inch diameter; which is the diameter of the 
