AND OTHER WATER WAVES 261 



at succeeding tides, and in most rivers is not seen 

 at every tide. The cinematograph representation, 

 on the contrary, can be repeated on the screen as 

 often as required, and with a delay of only one or 

 two minutes while the film is being re-wound. At 

 each repetition the observer can concentrate his 

 attention upon one particular feature. In this way 

 I have seen several things on the picture which 

 escaped my observation on September 29th. 

 Measurements can also be made from the film, 

 either in the hand or from its projection on the 

 screen. 



DESCRIPTION OF PLATES. 



(The figures are enlargements from individual pictures upon the 

 cinematograph film.) 



Fig. I shows the bore in the distance as a bright band, where 

 immediately before had been the dark image of bank and trees. 

 The 5-foot post is visible on the left, with its reflection below. 



Fig. 2 shows the boat rising to the wave. The wave on the 

 right of the boat cuts into two the reflection of the trees on the 

 right bank. A comparison with Fig. i shows at once the 

 turbulence of the water behind the bore. The alternation of 

 wide bright bands with narrow dark bands parallel to the front 

 of the bore indicates the character and position of the undula- 

 tions behind it, whilst the confused reflection of light near the 

 left bank indicates resurging therefrom. If the apparent heights 

 of the banks in the two figures be measured, the level of the 

 water will be found to have risen behind the bore. 



Fig. 3 shows the wave as yet unbroken, but with steeper front, 

 due to its approach to the shoal ; the inverted image is plainly 

 visible. Measurement of the post from the picture shows that 



