158 
There was no permanent set observable in any of the 
experiments, until the breaking weight was applied, the beam 
being allowed to recover itself on the removal of the load in 
each case. 
Each of the remaining beams was tested with a load of 
20 tons in the centre, the deflection varying from |ths to |ths 
of an inch. 
The calculations for the strength were based on the 
following formulae, given by Professor Hodgkinson in his 
“ Experimental Researches on the Strength and Properties 
of Cast Iron — 
First formula, art. 146 : 
Let W = the breaking weight in tons placed on the centre 
of the beam, 
a = the area of the bottom flange in inches, 
d = the total depth of the beam in inches, 
I = the length between the supports in feet, 
which gives 60.09 tons as the breadving weight of the beam. 
The second formula, art. 147, tadves into account the thick- 
ness of the vertical part of the beam, and is as follows : — 
Let W = the breaking weight in tons placed on the centre 
of the beam, 
I = the length between the supports in feet, 
b = the breadth of the bottom flange in inches, 
b' = the thickness of the vertical part in inches, 
d — the whole depth in inches, 
d' = the depth from the top of the beam to the upper si de 
of the bottom flange in inches, 
then W — 
In this case 
2.166 a d 
I 
a — 36, 
d = 24.25, 
I = 30.75, 
