CA\ADIAX FISHERIES EXPEDITION, 1914-15 



103 



order to render the picture of the scales as distinct as possible, a background of black 

 paper should be laid on the table to the right of the microscope. It will not be necess 

 ary to draw the entire contour of the winter rings; all that is needed is to mark tlu* 

 position of each ring along the edge of strip of a card, as shown in fig. 24. The can! 



Fig. 24. 



is laid on the table beside the microscope in such a manner that, to the eye, viewing 

 both card and scale in the mirror, the corner of the card falls exactly upon the centre 

 of the scale, the corresponding long side of the strip lying almost at right angles to 

 the basal line. If then each winter ring, and the margin of the scale, be marked off 

 along the edge of the card, a graph is obtained, presenting a magnified picture of the 

 growth of the scale. Multiplying all these dimensions by a factor which renders the 

 distance from the corner of the card to the mark for the edge of the scale equal to the 

 length of the fish — this can be easily done grai)hicany as shown in fig. 25 — we have 



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Fig. 25 



