use of this synchronous system is given in Section IV following. The timing 

 lights would function equally well for photographing wave phenomena through 

 the glass walls of a laboratory channel. 



Figure 12. Underwater Photograph of Synchronous Timing Lights. The octal 

 count is 0131, which equals 89 decimal count. Note the sand 

 ripples at base of grid. Grid dimensions are 10 cm (horizontal) 

 by 5 cm (vert ica I ) . 



The indicators themselves are No. 327 lamps. They are rated to be 

 powered from a 28-volt supply, but it was found that 18 volts applied to 

 the lamps increases their life appreciably and provides sufficient illu- 

 mination for underwater photography. The block of twelve lamps is sealed 



19 



