12 



BULLETIN OF THE BUREAU OF FISHERIES 



tank method and is placed in a glass tray of about 4 liters capacity. (Fig. 3.) The 

 end of the rubber tube inserted in the gill cavity is connected to a X tube, the upper 

 end of which is attached to a funnel filled with a fine suspension of carmine in sea 

 water. The third end of the tube is connected with a graduated glass tube (<) 6 

 millimeters in diameter and 17 centimeters long. Releasing the clamp {(J) a very 

 small amount of carmine is allowed to enter the tube, where it forms a distinct cone 

 moving inside the tube. The rate of movement of the apex of the cone is measured 

 by recording, with a stop watchj the tiihe required for it to pass from to the 15-centi- 

 meter mark. , i".-l 



Fig. 3.— "Carmme method" to measure the velocity of the current, a.— vertical tube with rubber connections; c— clamp; t.— 

 horizontal tube graduated in centimeters; «. — electric stirrer. The drawing is made from a photograph taken in the labora- 

 tory. Heating and aeration apparatus are not shown 



Inasmuch as a distinct cone of carmine suspension is visible, it may be assumed 

 that in this case we have a viscuous flow or stream line, to which the Poiseuille's 

 formula 



16fd- 



(1) 



is applicable. In this formula /§ = speed at the axis of the tube; Z> = diameter and I 

 length of tube in centimeters; A2? = pressure drop between the two marks in dynes 

 per cm''; /i = viscosity in poises. 



As the mean velocity S^ of the whole cross-sectional area of the tube is one-half 

 the velocity at the axis (see Gibson, 1925, p. 63) 





(2) 



