LOSS OF STRENGTH BY TWISTING. 23 
Dr. Robison has given an account of a very interesting experiment by 
Sir Charles Knowles, upon a piece of white or untarred rope, 34 inches in 
circumference. It was cut into many portions, and from each of those por- 
tions a fathom was taken off, and carefully opened out. It consisted of 72 
yarns, each of which was examined separately, and found to bear 901b. at 
an average for the whole. Each piece of rope corresponding to these was 
examined separately, and the mean strength of the same pieces was 4552 1b. 
Hence we have absolute strength of yarns = - . _. 6480 1b. 
Real strength 3 ; . 4552 
Loss of strength by twisting . : . 1928 1b. 
As the diminution of strength in the yarns, demonstrated by the preceding 
example, obviously arises from their position when twisted, in consequence 
of which they do not all bear the load at the same time; and not from any 
ermanent weakness produced by the twisting it became reasonable to be- 
ieve, that the twist given to ropes should be as moderate as possible. 
* * % % * 
The degree of twist commonly employed was such that the rope was two 
thirds the length of the yarns which composed it. M. Duhamel,’ who made 
many valuable experiments on this subject, in the royal dock-yards of 
France, caused some rope, to be worked with only ¢hree fourths of the length 
of the yarn. This last rope with the inferior degree of twist, bore 5187 lb., 
whereas the other bore only 43211b. He next caused these ropes to be 
made with different twists, and obtained the following results : 
Weight borne by each. 
Degree of twist. One experiment. Another experiment. 
3 4098 4250 
a 4850 6753 
4 6205 7397 
So far these experiments were highly satisfactory ; but it still remained to 
be seen, whether or not the ropes which had an inferior degree of twist, had 
not also an inferior degree of useful solidity, notwithstanding their supe- 
riority of strength in carrying weights. ; 
In order to determine this point, M. Duhamel had a considerable quantity 
of rigging made with yarns, wrought up into only three fourths of their 
length, and got them put into actual use on ship-board, during a whole cam- 
paign. The report given by the officers of the ship was highly satisfactory. 
They proved that the ropes thus manufactured were one fourth lighter than 
the common kind; that they were nearly one eighth more slender, so as to 
give less hold to the wind; that, from their being more pliant than the 
common ones, they run easier through the blocks, and did not run into what 
are teclinically called kinks; that the new cordage required fewer hands to 
work it, in the proportion of two to three; and that it was at least one fourth 
stronger. 
% * * * * 
Wherever ropes are not exposed to short bendings, as in the case of 
standing rigging, where they can be defended from water by tarring, é&c., 
the least twisted cordage may be advantageously employed, and should, 
according to M. Duhamel's experiments, be made from strands ; for it is de- 
monstrable that in fine stranded cordage, when the twist of the strands is 
1 ¢Traité de la Fabrique des Manceuvres pour les Vaisseaux, ou l’Art de la Corderie 
perfectionée.’ 
