8 4 SCIENCE PROGRESS 



ences in the " diameter " of lint-hairs, measured as the actual 

 width of the convoluted ribbons. This equivalence seems, 

 however, to hold good to a much less limited extent. Two of 

 the writer's pure strains had practically the same diameter, but 

 one was a typical " fine " cotton and the other decidedly robust. 

 The difference lay almost solely in the thickness of the cell-wall, 

 the fine cotton producing hairs which thickened their wall to a 

 smaller extent than those of the robust cotton. The former has 

 been spun satisfactorily to 180's count, 1 the latter only to 90's. 

 Consequent on these differences in wall-thickness, the breaking- 

 strain of the average hair in the fine cotton was much less than 

 in the relatively coarse one ; the difference was of the order of 

 57 grams in the latter to y6 grams in the former. 



Since the yarn from the fine cotton would be stronger than 

 that from the coarse one, if both were spun to the same count, 

 it follows from the above figures that the weakest hairs make 

 the strongest yarn, even when the diameter is constant. This 

 apparent paradox is actually quite reasonable, when we re- 

 member that yarn-strength depends mainly on the grip of hair 

 to hair, and is therefore — convolutions of the hairs being equal — 

 a function of the total Hair Surface per unit weight of cellulose, 

 which ratio is obviously greatest when the wall is thinnest. 



A further inconsistency has still to be eliminated from the 

 argument, for the expert grader of cotton knows that weak lint 

 is inferior lint. The difficulty here lies in the meaning of the 

 terms " weakness " and " strength " as used by the grader to 

 describe the manner in which a tuft of cotton has broken under 

 the strain applied by his hands. The terms cover a complex of 

 phenomena. A sample should break evenly, with a snap, and 

 not raggedly, if it is to be described as " strong," so that the 

 term embodies uniformity of breaking-strain. There is, further, 

 the question of friction : a tuft of lint may be quite unbreakable 

 in the hands, the tightest grip of thumb and finger being unable 

 to retain it up to the breaking-point, but if both ends of the tuft 

 are touched with sealing-wax it will break with ease, because 

 the hairs cannot then slip through the grip. Without entering 

 into further details, we can see clearly that the term " strength " 

 as used by the student of single cells, by the grader, and by 

 the spinner, has three entirely different meanings, so that no 

 objection to the writer's view can be raised by the grader on a 

 1 Count = number of hanks of yarn, each 840 yards long, from 1 lb. of cotton. 



