measurements on resonant bubbles. Hard-wall spherical 

 cavities may be particularly suited since the losses due to 

 the cavity are as small as possible and the influence of a 

 single very small bubble must be expected to be slight. 



To determine the effect of nuclei contained in plankton 

 may require that pure cultures be raised in the laboratory 

 so that the conditions under which the plankton is growing 

 can be established precisely. On the other hand it may 

 be possible to show by much simpler means that plankton 

 at least sometimes contain nuclei by exposing samples of 

 sea water to a vacuum and examining the water micro- 

 scopically before and after applying the vacuum. In this 

 fashion it may be possible to show with certainty that a 

 pressure reduction at times can cause plankton cells to 

 explode and to conclude that they contain nuclei. 



99 



