324 DR. FAIRS AIRN ON THE EFFECT OF IMPACT, YIBRATORY ACTION, 
sections should be respectively as 5 : 4 ; and the strain per square inch upon these parts 
will be respectively inversely as their areas ; that is, the strain per square inch upon 
the top section will be fths of the strain per square inch upon the bottom section. In 
one of the foregoing experiments, we have 
l , the length of the girder =2 40 inches, 
w, the weight laid on the middle=2-96 tons, 
a, the area of the bottom section =2 -4 inches, 
d, the depth of the girder=16 inches; 
therefore S== ~ 4x2-4 x 16 =4 ' 62 tons ’ 
the strain per square inch on the bottom section of the girder. 
Applying this formula to the whole series of experiments, we obtain the following 
summary of results : — 
Summary of Results. — 1st Series of Experiments. 
Beam 20 feet between the supports. 
No of 
experi- 
ment. 
Date. 
Weight on 
middle of 
the beam, 
in tons. 
Number of 
changes of load. 
Strain per 
square inch 
on bottom. 
Strain per 
square inch 
on top. 
Deflection, 
in inches. 
Kemarks. 
1 { 
From March 21st to 1 
May 14th, 1860 J 
2-96 
596,790 
4-62 
2-58 
•17 
2 { 
From May 14th to \ 
June 26th, 1860 J 
3-50 
403,210 
5-46 
3-05 
•23 
3 { 
From July 25th to 1 
July 28th, 1860 J 
4-68 
5,175 
7-31 
4-08 
•35 | 
Broke by tension at a 
short distance from the 
centre of the beam. 
The number of 1,005,175 changes was attained before fracture, with varying strains 
upon the bottom flange of 4-62 tons, 5-46 tons, and 7-31 tons per square inch. 
Beam repaired. — 2nd Series of Experiments. 
4 
August 9th, 1860 . . 
4-68 
158 
7-31 
4-08 
... { 
, The apparatus was ac- 
cidentally set in motion. 
5 
August 1 1th and 12th 
3-58 
25,742 
5-59 
3-12 
•22 
•1 
From August 13th, 1 
1860 to October l 
16th, 1861 J 
2-96 
3,124,100 
4-62 
2-58 
•18 
’1 
From October 18th, 1 
1861 to January 1 
9th, 1862 J 
4-00 
313,000 
6-25 
3-48 
•20 | 
Broke by tension as 
before, close to the plate 
riveted over the previous 
fracture. 
Here the number of 3,463,000 changes was attained when fracture ensued. 
