69 



contraction could of course be produced by the gradual burning 

 of some constituent of the cap which did not explode, but an 

 improbably large amount of such material would be required to 

 produce an appreciable effect while the bubble is large. During 

 the later stages of the contraction the measurements of the 

 radius may have been systematically too large, since the bubble 

 grew an opaque "beard". Near the maximum, however, the only 

 explanation of the asymmetry would seem to be the distortion of 

 the pictures by disturbance of the water surface or bending of 

 the mirror, as already mentioned. 



