296 On Chain Cables or Moorings, 



mechanical arrangement — an idea that a certain portion of 

 elaslicii}/ should be given to the chain. To attain this ideal 

 advantage, a certain degree of twist, equal to nearly one-fourth 

 of a revolution, was given to each link ; so that, when a strain 

 comes upon the chain, it never finds anv part of any portion of 

 it in that situation which would present the greatest resistance 

 to a change of figure. In such a chain, every strain makes an 

 effort to bring every link into tliat fprm which it ought to have 

 had in its first construction : and in proportion as the strain 

 effects this, so far the links have been weakened, by having the 

 particles of which they are respectively com))osed placed in a 

 new order, at the expense of the corpuscular attraction exerted 

 by these jiarticles individually for these to which they are most 

 contiguous. 



Tiiatthis derangement of ])articles, and consequent diminution 

 of strength, does take ))lace in twisted links, is plain from 

 what happens in j^roving the chains composed of such links : " a 

 cable for a ship of -400 tons will stretch during this operation, 

 in a whole cable nearly thirty foe t ! and will recover about 

 ien''^'," when the strain is taken off! What a derangement is 

 here ! When we look at this, and contemplate the injury hereby 

 inflicted on the materials, we confess that we are not surprised 

 that some of these chains have given wa>'. That any of tlieni 

 should stand after sustaining such an injury, furnishes, perhaps, 

 the strongest evidence that could he adduced, of the juperiority 

 of iron over hemp for the purposes of a cable. 



It is the more surprising that Captain Brown should have 

 fallen into this mistake respecting elasticity, having himself de- 

 tected and exposed its fallacy as to hemp : "There cannot (says 

 he) even be any certain advantage deduced from the portion of 

 elasticity which cordage is known to possess ; for the force 

 which caused its extension may be extended for a considerable 

 time after the cable has been stretched to its utmost hmits :'' — 

 of course, under a fiirtlier strain it must break. He might have 

 added, that every lengthening of a rope by strain is accompanied 

 with the rupture of a certain number of its fibres : every re- 

 petitimi of the force ruptures more of them, and thus in time it 

 becomes unserviceable. There is no stretching without this 

 partial rupturing : and it is equally true, that no change in the 

 relative position of tlie particles of matter in the link of a chain 

 can be induced vvithout a proportionate rupturing, injurious to 

 its strength, taking place, tliough not perceptible to the eye. 



Were it even true that the giving of a hempen cable was in 



* Observations on the Pateut Iron Cables invented by Captain Samuel 



itf 



