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Fresh-water Biology 



E. DEMONSTRATIONS 



Study 22 

 THE EFFICIENCY OF STREAM-LINE FORM 



Take a double handful of grafting wax* and manipulate it until it becomes plastic 

 under the warmth of the hands. Embed a slender wire in the middle of the wax, anchoring 

 it there to a centrally located button. Make a loop in each free end, for attachment to 

 the hook of a delicate spring balance. 



Then mold the wax successively into each of the four forms suggested below, suspend 

 it on the balance, lower it into a swift, smoothly flowing current of clear water in a chute 

 or trough, and observe the pull: 



1. A cone whose section is an equilateral triangle, with the wire in the axis of the cone. 



2. An oval (that of a hen's egg) with the wire in its long axis. 



3. A mass in the form of a sunfish with the wire in its long axis. 



4. A mass in the form of a trout with the wire in its long axis. 



Do not alter the amount of wax during the experiment; only change its form. The 

 indicator of the spring balance will oscillate about a mean which is the normal pull, 

 measuring resistance of the current. 



For Record: 



This may be set down in figures as follows: 



1. Pull on cone, direct grams; reversed grams. 



2. Pull on oval, direct grams; reversed grams. 



3. Pull on sunfish, direct grams; reversed grams. 



4. Pull on trout, direct grams; reversed grams. 



* Grafting wax may be purchased from dealers in horticultural supplies. It may be made as follows: 



Rendered tallow 1 part 



Beeswax 2 parts 



Rosin 4 parts 



Melt together with moderate heat; pour into a pail of cold water; pull (like taffy) until light colored. Smear 

 hands with tallow while pulling. 



