horizontal bubble lines is that of the vave length of the kixik in the 

 kinked wire. Increasing or decreasing this spacing is therefore achieved 

 by suitably adjusting this wave length. A photograph of a spider-web 

 bubble pattern can be seen in the wake of a circular cylinder in "Figure 4. 

 Note that an analysis like that described above can be performed only when 

 the two bubble-generating wires are positioned as shown in Figure 3a. The 

 wire configuration shown in Figure 3a and the previously described analysis 

 were successfully employedj, and results can be seen in Reference 6. 



Another way of achieving these intersecting patterns of hydrogen 

 bubbles is accomplished without the use of kinked wires. If straight 

 (O.OOl-in. diameter) wires ■ energized with dc excitation are installed like 

 rungs in a ladder (Reference k) in the flow so that the line of vision is 

 parallel to the rungs^ the steady sheet of bubbles from each wire rung appears 

 as a line to the observer. Positioning another wire in the usual manner 

 (shown in Figure 3^)^ i.e., perpendicular to the direction of vision, enables 

 creation of the transverse rows of bubbles such that an Intersection of 

 bubble lines is visible. Additional intersections are obtainable with 

 additional wires. The wires installed as ladder rungs which are oriented 

 parallel to the direction of vision do not have to produce bubbles along 

 their entire length to create these intersections. Wires which are 

 coated with a thin waterproof insulator except for some small interval 

 at the center of the wire suffice for the production of a bubble line as 

 seen by the observer. It is important that the insulation be thin to 

 avoid vorticity shedding from the insulated portions of the rungs . The 

 wire which receives pulsed excitation (viewed perpendicular to its length) 

 can then be positioned in or out of these ribbons of bubbles. Such a scheme 

 has several advantages . One is the lifting of the velocity limitation due 

 to the shedding phenomena behind the 0.004-in. diameter kinked wire. Another 

 is the flexibility of choice of spacing between the longitudinal lines . 

 Positioning the transverse wire in the sheets of bubbles streaming from 

 the rung wires also enables visual determination of whether or not vortex 

 shedding is taking place from the transverse wire, i.e., for R )• 4o. 



