Cavity Supports 



The rubber supports shown in figure 1 were not very 

 satisfactory. The cavities had to rest on a large area of 

 the support in order to assure stability. Wire supports 

 were attempted and these resulted in the improvement of 

 the Q factor but made cleaning of the side -walls quite diffi- 

 cult. A further difficulty was that the whole cavity would 

 oscillate like a pendulum at a low frequency, and thereby 

 set up wave motion on the rather large free water surface. 



The supports finally adopted, and used throughout the 

 data collection, did not have any of these shortcomings. 

 They consisted of four pieces of angle aluminum. The line 

 of support was approximately ^ inch from the extreme 

 corner of the cavity (fig. 2). No increase in the total 

 cavity loss occurred if the supports were moved away from 

 the corners by as much as an additional ■§ inch. This was 

 regarded as evidence that the loss due to this type of sup- 

 port was insignificant. In any event, the residual loss 

 caused by the supports if present is taken into account in 

 the calibration of the cavity with distilled water. The 

 aluminum angle supports were used throughout the data 

 collection phase of the work reported here. 



Power Supply to Cavity 



Different methods of driving the cavities were tried in 

 order to minimize the losses due to the transducers, and 

 at the same time obtain as convenient an instrument as 

 possible. Provision of power input direct to the cavity 

 wall was attempted by gluing a ring of radially polarized 

 barium titanate to it and touching the side with a point 

 driven by a specially constructed electromagnetic system. 

 However, the cavity Q was degraded seriously by this 

 procedure. The simplest driving methods proved to be 

 the best. Two small transducers made from barium 

 titanate cylinders were immersed in the water close to 



16 



