on the Strength of Materials. 167 
results. The difficulty consists in assigning a value to the dif- 
ferent degrees of diminution. When compressed beyond a cer- 
tain thickness, the resistance. becomes enormous. 
Experiments on the Suspension of Bars. 
The lever was used as in the former case, but the metals were 
held by nippers, as indicated in the drawing No. 2. They were 
made of wrought iron, and their ends adapted to receive the 
bars, which, by being tapered at both extremities, and increasing 
in diameter from the actual section (if I may so express it), and 
the jaws of the nippers being confined by a hoop, confined both. 
The bars, which were six inches long, and 1 square, were thus 
fairly and firmly grasped. 
No. April $0, 1817. 
45 4 inch, cast-iron bar, horizontal ‘%. 1166 Hess 
46 : do. do. vertical sib: ak 
47 ; do. cast steel previously tilted .. 8391 
AS ; do. blister steel, reduced per hammer 8322 
49 : do. shear steel, do. do... sshd GA 
50 4 do. Swedish iron, do. do. -. 4504 
51 i do. English iron, do. do. os 3492 
32 7 do. hard gun-metal, mean of two trials 2273 
93 3 do. Sate copper reduced Perl oie 
ammer .. He ony 
54 j do. cast copper of sa 0192 
55 ; do. fine yellow brass .. ale) hoe 
56 4 do. cast tin .. ae Rible PaO 
37 i do. cast lead ale Pe bad a! 
Remarks on the last Experiments. 
The ratio of the repulsion of the horizontal cast cubes to the } 
cohesion of horizontal cast bars, is 8°65: 1. 
The ratio of the vertical cast cubes to the cohesion of the ver- 
tical cast bars, is as 9°14: L. 
The avetage of the bars, compared with the cube, No. 16, is 
as 10-611: 1. 
The other metals decrease in strength, from cast steel to cast 
Jead. 
The stretching of all the wrought bars indicated heat *. 
The fracture of the cast bars was attended with very little di- 
minution of section, scarcely sensible. 
The 
* Mr, Rennie’s apparatus did not permit of measuring the extension of 
the specimens. In some experiments made by Mr. Telford, (Barlow's 
Essay on the Strength of Timber, &c. p.230,) where the extension was mea- 
sured, it appears to have been greatest at the middle of the length, and to 
L 4 increase 
