had to be recorded photographically and then analyzed statistic- 

 cally The present method has the advantage that the statistical 

 analysis is bypassed since average quantities are measured directly. 

 On the other hand, it has some disadvantage in that the operation 

 of measurement alters the quantities being measured and makes 

 substantial correction necessary 



OUTLINE OF 



The idea of the method will be briefly described before pro- 

 ceding to a more detailed description of experimental procedure* 

 A schematic diagram of the equipment is given in Figure 1«, In a 

 turbulent stream of water a small element of dye emitted from the 

 injector will tend to meander from the axis of the injector in an 

 erratic fashion following the erratic motion of the water» Ele- 

 ments leaving the injector at different times, not too close to- 

 gether, will generally follow quite different pathso If the 

 sampler is now fixed in some definite position and a sample of 

 the water passing by withdrawn through it at a uniform rate over 

 a sufficiently long time interval, the resulting sample will be 

 more or less strongly colored depending upon how frequently ele- 

 ments of dye are carried as far off the axis as the sampler is 

 situated o One expects the greatest density of dye if the sampler 

 is right on the axis and steadily decreasing amounts as it is 

 moved off the axis If the sample is taken over too short a time 

 interval, the sample may give a concentration of dye deviating 

 too much from the true average % it is conceivable that such a 

 sample might be almost pure water or almost piye dye, depending 

 upon the short time interval In which the sample was taken. The 

 actual concentration of dye was measured by means of an electro- 

 photometer which had been calibrated for the dye being used. 

 However, it is not difficult to think of other schemes for doing 

 the same thing e 



If the turbulence of the water is very intense, one will 

 expect the dye elements to wander farther from the axis, on 

 the average, In a given distance downstream,, than if the turbu- 

 lence is not very Intense Consequently, the rate of spreading 

 of the average dye wake gives a measure of the intensity of 

 turbulence near the end of the injector,, The discussion of the 

 method for obtaining a quantitative measure of the turbulence 

 is described in the section dealing with the analysis of the 

 datao 



In the case of heat diffusion behind a heated wire it is 

 necessary to make a correction for the molecular diffusion of 

 heat which is taking place as well as the turbulent diffusion. 

 In the case of dye diffusion the molecular diffusion can be 

 completely neglected, for the amount is very small during the 

 time intervals involved . 



