84 DEPARTMENT OF THE l^ATAL SERVICE 



transparent plastic mass, as, for instance, collodium solution. The scale is glued to 

 a glass plate, with its inner sidd next the glass, a small quantity of collodium is 

 poured over the whole, and the glass set aside in a slanting position, to dry. After a 

 short time, when still soft, the collodium may be removed in the shape of a thin film, 

 in which will be found an impress of the surface of the scale. Plate III, fig. 3, shows 



Plate II. 



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'<■■ / 



FIG, 2 



a photographic reproduction of a part of such an impression, together with the corres- 

 ponding part of a photograph of the scale itself. All details are distinctly visible in 

 the plastic impression. From this experiment we may with perfect certainty conclude 

 that the picture presented to the eye when observing a herring scale through a low- 

 power lens, is nothing but the play of light on the surface of the scale, which is thus 

 found to be moulded in delicate and detailed relief. The visible winter rings and 

 summer zones, like the fine stripes, the basal line, and the centrepoint, all belong 

 solely to the surface of the scale. 



