506 - 2- 



remained open for about i second. 

 Location of the Charge . 



The charge was suspended, detonator underneath, at a depth of 3 feet in a total deoth of water 

 of 9 feet 6 inches. In most cases a rigid steel rod franework was fixed in the .plane of the charge; 

 this served as a reference framework in the photographs giving both a length scale and a fixed reference 

 point from which the movement of the bubble could be determined as well as its size and shape. 



In order to obtain a satisfactorily large image of the bubble when near its minimum, it was 

 necessary for the camera to be about 5 feet from the charge. At this distance the field of view was 

 a circle of »bout 30 inches diameter; accordingly the reference framework had to be well within the 

 volume occupied by the bubble when large. The framework was therefore made of small enough section 

 to produce a negligible disturbance of the bubble motion. A number of photographs were taken with no 

 framework present, and the bubble shape and size were exactly the same as when a framework was used. 



For photographs of the bubble near its maximum size the camera was 8 feet away, and the field 

 of view about u feet diamst>?r so that a more rigid framework with its members further from the centre 

 of the bubble could be used. 



Method of Measuring the Photographs . 



(a) Volume of the Bubble :- It was assumed that, apart from small protuberances and needle- 

 like projections, the bubble was symmetrical about a vertical axis through its centre. The horizontal 

 diameter of the profile of the bubble was measured at a number of equally spaced levels along this axis 

 of symmetry - any small asyrmetrical bumps on the profile being ignored as containing a negligible 

 volume. The squares of these diameters wore then sumned, the intervals being small enough to justify 

 this. 



It will be observed later that when the bubble is very close to its minimum its upper surface 

 appears to be actually concav^?. This "mushrooming" of the bubble has been observed by Taylor with his 

 •micro-scale" spark bubbles'. The profile of the bubble no longer coincides with the cross-section - 

 the profile shows only' the rim of the "saucer"-l ike depression at the top of the bubble. However, the 

 bubble is not completely opaque and it Is thought that the upper boundary of the "splash" of light coming 

 through the centre of the bubble, which has been seen on some previous photographs, marks the lower edge 

 of this hcUow depr«sf ion in the bubble. Hence an a proximate shape to the cross-section of the bubble 

 may be sketched in and its volume computed. 



The apparent diameter of a sphere viewed at a finita distance is always less than its true 

 diameter. This difference can be allowed for quite simply from geometrical considerations and in the 

 present experiments only amounts to 2* for the largest bubble diameters, 



(b) The pDtition of the "Centre ' Gravity" of the Bubble :- The position of the "centre of 

 gravity" of the volume occupied by the bubble was calculated by taking moments of the squares of the 

 horizontal diameters about any convenient horizontal line. The chief error involved in determining 

 the total displacement of the bubble lies in uncertainty as to the absolute position, relative to other 

 objects in the photograph, of the point where the Charge was detonated. Errors in setting the depth 

 of the Charge were of the order of i inch and a random error of this order is inherent in every 

 measurement of the displacement of the bubble. 



(c) 



The mcticn and shape cf the hollow produced by an explosion in a liquid. 

 G I. Taylor and R. M. Oavies. 



