OTHER PROPERTIES OF CAST IRON. 269 
From the above table or compendium, it 
appears that we have 581lbs. for the greatest 
strength, as obtained from the Ponkey iron; and 
357|bs. for the weakest, as in the Plaskynaston: 
equal to 469 asa mean of the twoextremes. Or, 
taking a general mean of the whole irons 
experimented upon, we have 445.6 as the ave- 
rage value of strength. This number is pro- 
bably the nearest approach to the transverse 
strength of cast iron yet given to the public; 
it is deduced from experiments on nearly the 
whole of the British irons, and must, from the 
variety, accuracy, and number of experiments 
given in the preceding pages, be considered as 
a fair average value. Taking it therefore 
as the representative of the transverse strength 
of a rectangular bar of cast iron, 1 inch square, 
4ft. 6in. between supports; and comparing it with 
the experiments of previous writers on the same 
subject, we have, instead of approximate results, 
considerable differences and anomalous contra- 
dictions to contend with. These differences 
are not exclusively applicable to the experi- 
ments now under consideration, but variable 
as respects the conclusions of the experimentors 
themselves. 
