866 
ME. HODGKINSOjST’S EXPEEI3IEXTAL EESEAECHES 
From the present experiments on pillars whose models were 2^ inches diameter 
in most cases, Tables I. to Yl. 
Diameters of 
pillars 
compared. 
Lengths of 
pillars 
compared. 
Values of x. 
Mean values 
of X. 
Remarks. 
in. in. 
21 and 2|- 
21 and 2-^ 
2|- and 2^ 
2^ and 2^ 
21 and 2j 
2j and 21 
2i and 2} 
and 
and 
21 and 2j- 
2^ and 2^ 
ft. ft. 
10 74 
10 
10 6i 
10 6i 
10 64 
10 6i 
10 6i 
10 6i 
10 6| 
10 5 
10 5 
1*6303* 
1*8864' 
1*5737 
1*5514 
1*4137. 
1*482 ' 
1*4752 
1*8338 
1*8986 
1*4523" 
1*5942, 
d 
1*6303 
1*6063 
1*6724 
1*5232 
* This result is a mean from ten comparisons 
on different kinds of iron. Tables II., III., lY. 
’’ From four kinds of iron, Level, London 
Mixture, Old Hill and Derwent. Tables III. 
and V. 
^ From the Second London Mixture. Ta- 
bles III. and V. 
From Old Hill Iron. Tables III. and VI. 
Mean value of x from all the comparisons, twenty-five in number, 1*6285. 
In the former experimental paper, mentioned above, I assumed 1-7 as the inverse 
power which the strength of pillars of the same diameter and of different lengths 
followed nearly, this applying both to pillars with rounded ends and to those with flat 
ends ; but it appears from above, that in flat-ended pillars, representing the great mass 
of those used in practice, the strength would be better represented by some number 
intermediate between 1’6 and 1'7 ; the results of the experiments here detailed give 
1-63 as a mean nearly, and this number may be used for all pillars whose length is more 
than about thirty times the diameter. In pillars shorter than this the formula used for 
calculating their strength would require correcting, as previously mentioned in page 859. 
Strength of Pillars^ the Iron in the section of which is not uniform. 
The iron of all the pillars in this research is assumed to be uniform and of equal 
resistance throughout the surface of fracture, but this is perhaps seldom or never the 
case in cast iron, except possibly in very large castings. My experiments on the crush- 
ing of cast iron, made for the British Association, to determine the relative values of 
hot and cold blast iron *, of which an abstract is given in my ‘ Experimental Eesearches 
on the Strength and other properties of Cast Iron, 1846f,’ showed that small cylinders of 
cast iron. No. 2, from the Carron Iron- works, turned to the exact dimensions from cast- 
ings made but little larger than the size intended, required to crush them 130163 lbs. 
per square inch when they were inch diameter, and 132319 lbs. per square inch when 
they were f inch diameter, from means of several experiments. In cylinders and prisms 
cut out of larger masses, the crushing weight per square inch was reduced to 119730 lbs., 
103012 lbs., 102884 lbs., 108315 lbs., 96764 lbs., &c. In the experiments made to 
determine the crushing strength of the iron in my former experiments on piU.ai-s;|:, cylin- 
ders '52 inch diameter and nearly of the size of the original casting, requii'ed 115910 lbs. 
* Seventh Eeport, 1837. f Weale, London. 
X Philosophical Transactions, 1840, Part II. p. 419. 
