ON THE UNION OP FLEXIBLE FIBRES. 181 



is to the weight, as twice the circumference to the diameter; supposing, for 

 example, that the friction of rope on metal were one tenth of the pressure, 

 then a single coil of rope round a cylinder of metal would support about two 

 thirds of the weight; or if the weights acting on the different ends are dif- 

 ferent, the adhesion may be a little greater or less than in this proportion, 

 according to the manner in ■'.vhich the rope is applied. If such a rope 

 made two or three coils, it would be impossible to apply a force sufficient 

 to cause it to slide in the grooves. * 



From considering the effect of a force which is counteracted by otker forces 

 acting obliquely, we may understand both the effect of twisting, in binding 

 the parts of a rope together, and its inconvenience, in causing the strength 

 of the fibres to act with a mechanical disadvantage. The greater the obli- 

 quity of the fibres, the greater will be their adhesion, but the greater 

 also will be their immediate tension, in consequence of the action of a 

 given force in the directioii of the rope: so that after employing as much ob- 

 liquity and as much tension, as is sutBcient to connect the fibres firmly, in 

 all cases of relaxation and of flexure, and to prevent in some measure the 

 penetration of moisture, all that is superfluously added tends to overpower 

 the primitive cohesion of the fibres in the direction of their length. 



The mechanism of simple spinning is easily understood; care is taken, 

 where the hand is employed, to intermix the fibres sufficiently, and to en- 

 gage their extremities as much as possible in the centre; for it is obvious 

 that if any fibre were Avholly external to the rest, it could not be retained in 

 the yarn; in general, however, the materials are previously in such a state of 

 intermixture as to render this precaution unnecessary. Where we have a 

 number of single continuous fibres, as in reeled silk, they are sufficiently con- 

 nected by twisting, and we have no need of spinning. In both cases such 

 machinery has been invented for performing the necessary operations, as is 

 both honourable and lucrative to the British nation. 



A single thread or yarn, consisting of fibres twisted together, has a ten- 

 dency to untwist itself; the external ptrts are the most strained in the opera- 

 tion, and at first shorten the thread, until the internal parts have no lonj?;er 

 roam for spreading out laterally, as, they must necessarily do when their 



