SEA-FISHERIES LABORATORY. 339 



The upper surface carries a stout brass pillar, upon which 

 slides a square block which can be clamped in position by a 

 thumbscrew. To the inner surface of this block is attached 

 a curved arm, carrying a tightly-stretched wire. This arm 

 is hinged to the block, the hinge being accurately adjusted, 

 so that when the arm is moved up or down the wire always 

 travels in the one plane perpendicular to the surface of the 

 board. Owing to this hinge, and to the sliding of the block 

 upon the pillar, this wire can be accurately adjusted to any 

 desired position upon the body of the fish, whatever its thick- 

 ness. Then one looks down upon the wire, in line with the 

 pointer below, when the desired measurement is read off 

 accurately upon the scale. 



In actual practice we have found it desirable to set the 

 wire by means of a line ruled across the board perpendicular 

 to the edge of the scale. It is seldom necessary to move the 

 block on the pillar ; unless the fish vary very greatly in thickness 

 the swinging of the arm affords all necessary clearance. 



We have found this board very satisfactory, as it is both 

 accurate and rapid in use. 



