METHODS OF INVESTIGATION 187 



obtained very quickly. The fibres are mounted in a 

 parallelized tuft, and observed in the middle of the tuft, 

 or elsewhere as may be desired, and an H- shaped mark 

 made on the drawing paper to define the two margins of 

 each fibre, the cross-bar of the H tying together the two 

 parallel margins in order to prevent confusion. The 

 magnification should be so adjusted that each H is not 

 less than 10 millimetres wide, and the mean width can 

 then be taken with a millimetre scale, or by a simple form 

 of instrument for totalling small lengths, which consists 

 of a lever bearing a stylus and revolving a drum by means 

 of a friction ratchet, or where cheap labour is available 

 by cutting out each H from the paper, and placing 

 them edge to edge in a row. 



Weight. The comparison of weight of equal lengths 

 of fibre might be exceedingly useful, but until we can 

 devise a machine which will count single lint hairs it must 

 remain impracticable,* on account of the strain on the 

 eyes, which is far worse than in isolating single fibres. 

 When impact- testing of strength is employed, the two 

 may be combined, and the fibre- counting necessitated by 

 the one be utilized for the other. 



Some seventy to a hundred fibres having been counted 

 out, they are fixed across a gap in a piece of stout paper 

 under slight tension by a drop of sealing-wax at either 

 end. Twenty millimetres are then cut out of the centre 

 by scissors, or by two safety razor blades mounted parallel 

 in a brass holder. The bunch of 2-centimetre lengths thus 

 obtained is bundled up and hung on the hook of a micro- 



* See, however, note on p. 102. 



