Fail by crushing with length under............ 6 diameters.

Principally by crushing from...................... 5 to 15 "

Partly by crushing, partly by bending, from. 15 to 25 " Altogether by bending above..................... 25 "

Cast iron of average quality is crushed with..... 49 tons per sq. in.

Wrought iron of average quality is crushed with 16 " '•

Wrought iron is permanently injured with....... 12 " "

Oak wrought is crushed with......................... 4 " "

Deal wrought is crushed with........................ 2 " "

The comparative strength of different columns, of different lengths, will be seen very clearly from the following table derived from experiments by Mr. Hodgkinson:

Wrought Iron Bars.

Proportion of Length to Thickness.

Gave way with

Square.

Length.

ins.

1 X 1

ft. ins.

7½ to l

21.7 tons per sq. inch.

It

1 8

15 to 1

15.4 "

II

2 6

30 to 1

11.3 " "

<<

5 0

60 to 1

75 " "

II

7 6

90 to 1

4.3 " "

½ X ½

5 0

120 to 1

2.5 " "

"

7 6

180 to l

1. " "