116 
FIFTH REPORT— 1835, 
The bodies struck above were all single balls of cast iron, 
with the flat piece of lead laid upon them. 
To ascertain the strength and extensibility of this wire, it 
was broken, in a very careful experiment, with 2524 lbs. sus¬ 
pended at its lower end and laid gradually on. And to obtain 
the increment of a portion of the wire (length 24 feet 8 inches) 
when loaded by a certain weight, it had 139 lbs. hung at the 
bottom, and when 89 lbs. were taken off that load, the wire de¬ 
creased in length *39 inch. 
Whence 89 lbs, : ‘39 : : 252’5lbs, : XT2 inch = the ultimate 
extension of 24 feet 8 inches. 
1*09 inch = ultimate extension of 24 feet, or extension 
of that length of the wire when loaded to its breaking point. 
Remarks.—1st. Should it be suggested that the wire by being 
frequently impinged upon would perhaps be much weakened, 
the author would beg to refer to a paper of his on Chain Bridges, 
Manchester Memoirs , 2nd series, vol. v., where it is shown that 
an iron wire broken by pressure several times in succession is 
very little weakened, and will nearly bear the same weight as at 
first. 
2 nd. The first of the preceding experiments on wires are the 
only ones from which the maximum can, with any approach to 
certainty, be inferred; and we see from them that the wire re¬ 
sisted impulsion with the greatest effect when it was loaded at 
bottom with a weight which, added to that of the striking body, 
was a little more than one third of the weight that would break 
the wire by pressure, a conclusion which does not differ widely 
from that of Cor. to Prob. 4, 
3rd. From these experiments generally, it appears that the 
wire was weak to bear a blow when lightly loaded. 
These last experiments and remarks, and some of the pre¬ 
ceding ones, show clearly the benefit of giving considerable 
weight to elastic structures subject to impact and vibration ; and 
the weight of greatest resistance may frequently be calculated 
from the formulae in problem 4 or its corollary. 
