the recognition in the medical field of phenomena which may be included in the field of cavi- 

 tation has provided yet another incentive for research. For example, interest in the inception 

 and subsequent behavior of small, individual cavitation bubbles arises in connection with the 

 general medical problem of gas separation in living tissue (see, e.g., Reference 1*) of which 

 a special problem is the phenomenon of deep-sea divers' "bends" in which gas separates 

 from the blood stream during too-rapid decompression. Again, there is interest in the medical 

 field in the type of cavity formed during the air-water entry of a projectile since the wounds 

 produced by missiles evidently behave as such cavities during the entry phases (see, e.g., 

 Reference 2). 



Although many questions remain to be investigated before the mechanism of cavitation 

 phenomena can be more completely understood, much progress has been made toward rational 

 descriptions of the processes in cavitating systems. This work includes not only the hydro- 

 dynamics of flows with both liquid and gas or vapor phases, but also the physical chemistry 

 of such multiphase flows in relation to the formation, collapse, and maintenance of cavities. 

 In a previous report,^ the writer attempted to outline very briefly and approximately the status 

 of knowledge of various cavitation problems up to the year 1950. In that report, an attempt 

 was also made to indicate some of the relationships between cavitation and other hydrodynam- 

 ic phenomena and between the various types of cavitation in a somewhat more systematic way 

 than had been done previously. Because of the constantly growing need among naval archi- 

 tects and engineers for more precise data on cavitation, it seems worthwhile to bring up to 

 date the discussions of Reference 3 with the purpose not of providing design data for specific 

 problems but, primarily, of providing background information necessary in the development of 

 rational design criteria, procedures, and evaluations.. 



Although the present work is intended primarily as a survey of recent progress, an 

 attempt will also be made to indicate the various problems and factors that, in the writer's 

 opinion, require further study and to indicate how these problems arise by following an outline 

 based on the sequence of events in the establishment of cavitating flows. This requires de- 

 finitive terms for the "types" of cavitation, discussion of inception and of the processes in 

 these various types of cavitation as well as of the types to be expected in any given system. 

 Of necessity, some of the material in Reference 3 will be repeated, but, in general, liberal 

 reference will be made to that work in preference to repetition. In this short paper, it will 

 not be possible, of course, to give many details of recent investigations. However, it is 

 hoped that not too many available references have been overlooked. 



♦References are listed on page 21. 



