OF NITRO-CELLULOSE AND THE LAW OF ITS OPTICAL BEHAVIOUR.' 
157 
Fig. 13. Stress bands in spectrum load - IS lb. B.mt. 178*3 Ib.-inches. 
If then the mean distances of the bands are plotted as ordinates against the order 
of the band as abscissae, fig. 14, a convenient form of diagram OOF is obtained in 
rectangular co-ordinates X, Y, in which Y is the distance from the neutral axis to a 
scale a and f is the stress to a scale (3, or 
y = Y . a ; / = X . j3, say. 
z 2 
