Abstract
The general problems encountered in determining the number and average size of a population of opaque particles randomly distributed on a transparent or translucent ground are discussed, with particular reference to the use of optical scanning methods for such determinations. An apparatus suitable for scanning specimens of carded webs, with a view to determining their nep content, is described, and it is shown that, when used with "ideal" samples consisting of small black paper disks randomly distributed between glass plates, it is capable of counting and sizing the particle array within very close limits. The particular difficulties encountered with carded web samples are then discussed with reference to actual experimental results, and a method of computing the "neppiness index" is described. It is suggested that this index may be a more reliable and consistent measure of the neppiness of a sample of carded web than the "nep count" which has hitherto been used for this purpose.
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