643 



S ^^^ - 2^ (2) 



^. 



which is more realistic than Eq. (l), may easily be deduced. T is exactly 

 equal, of course, to the tensile strength of the water and, under such con- 

 ditione that Vq becomes just equal to zero, this equation provides a means 

 of determining the force necessary to rupture water under the conditions of 

 the experiment. Any means of determining T is interesting because a know- 

 ledge of this value is very desirable and not easily determined. 5) 



Although Eqs. (1) and (2) derive from pure hydrodynamics^*^) the 

 derivations take no account of possible variations of such fundamental 

 properties as surface tension and viscosity. It would seem desirable to 

 investigate the effect on the dome velocity of varying these properties. 

 This should give us a better insight into the thermodynamic behavior of the 

 liquid medium under such conditions. The present work includes a study of 

 surface tension effects as well as the effect of spreading oil slick on the 

 surface. The limitations of time and film consumption prevented continuing 

 the work into a program to study viscosity variation. It is hoped that this 

 work will be continued. 



II. EIPEHIMENTAL 



1. Pond Work 



The experiments were performed in the fresh water pond on Nonamessett 

 Island. The relative position of the various units of the recording equip- 

 ment is best seen by reference to Fig. 1. For most of the shots, two 

 cameras were used to record the velocity of the rising dome. To record the 

 "streak" type of picture, a General Radio type 65I AE oscillograph recorder 

 using 35 mm film was used on all shots. The camera was mounted on its side 

 (with the film moving horizontally) about a foot above the water surface. 

 A vertical slit 0.1 in. wide was placed in front of the focal plane in order 

 to narrow the field of view and thus produce a more clearly defined record 

 of the edge of the image formed by the rising dome.2»b) To understand the 

 phenomena better, and to obtain a different sort of record for measurement, 

 a Fastax 35 mm camera was also used for almost all the shots. This camera 

 was also placed on its side so that the rising dome would be photographed 

 along the long dimension of the frame. This introduced another simplification 

 of measurement because lines could be drawn through a succession of frames 

 to e3tabli3h a common base line and slope of rise velocity. Timing marks 

 were put on the edge of the film in the General Radio camera by means of a 

 spark coil energized by an electronically amplified pulse from a 100 cycle 

 tuning fork. In the Fastax camera, 1000 cycle timing marks were marked on 

 the edge of the film by means of the timer described by Cole, Stacey, and 

 Brown. K) 



