22 LOSS OF STRENGTH BY TWISTING. 
It was long ago shown by Dr. Hooke, from several experiments He ie 
strength of cordage in 1669, that the strength of the component parts o t 1e 
rope was diminished by twisting. This fact, indeed, has been long practi- 
cally known to sailors, who are familiar with the superior strength of rope 
yarns when made up into a salvage, which is nothing more than a skein 
without twisting. Salvages are invariably used for slinging great guns, 
rolling tackles, and for every kind of work where great strength and great 
pliancy are required. 
In the ‘Memoirs of the Academy of Sciences,’ M. Reaumur 
has given an account of his experiments on the strength of 
ropes compared with that of their parts. 
2. The yarn of a skein of white thread bore each, at an average, 93 lb. 
Two yarns twisted slack into a cord broke with 16 lb. 
Hence we have the absolute strength of two yarns . . 19$]b. 
Real strength . : . : - 16 
Loss of strength by twisting . : . 33]b. 
8. The average strength of some thread was such, that each broke with 
8 lb., whereas when three were twisted they bore only 173 1b. 
Hence we have absolute strength é . ‘ . 24 Ib. 
Real strength . : F . 173 
Loss of strength by twisting . ‘ . 631b. 
4, The average strength of some thread was such, that each broke with 
74 lb., whereas when four were twisted they broke with 213 lb. 
Hence we have absolute strength F : . 30 1b, 
Real strength : Its 3 : i . 215 
Loss of strength by twisting : . 83lb. 
5. The average strength of other four threads was such that each broke 
with 9lb., whereas when twisted, they broke with 22 lb. 
Hence we have absolute strength . 86 Ib. 
Real strength . : . » 22 
Loss of strength by twisting . : . 14]b. 
6. A well made and small hempen cord broke in different places with 58, 63, 
67, and 72 1b., so that its average strength was efor Wait Gy ate 65 Ib. 
The cord ponsites 7 three strands, and another part of it was untwisted, 
and its three strands separated. One of them bore 29: 
a ae 3, another 334, and 
Hence the absolute strength of the three strands, wh i 
Real strength when twisted : : - oe a iercae i“ . ‘ke 
Loss by twisting : - 33 1b. 
7, Another part of the same cord, which broke with 72 1b 
into its strands, when they bore 26, 28, and 30 pounds : 
Hence we have absolute strength : : 841b 
Real strength : ; ' ee; ae 
» Was separated 
Loss by twisting : - 121b, 
