76 



MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



lei to AX, the lines of resistance AB, AC, AD, AE, AF, and AG, being formed 

 from the Analysis of the Experiments of 1835, in pp. 100 and 101. 



Fig. 10. 



4 5 6 7 



8 9 



y 



10 n 12 13 14 15 16 17 10 ly zo 



Y 



Section VIII. — Practical Applications and Illustrations of the Law of the Wave 

 in the Navigation of Rivers and Shallmv Water. 



Experienced river boatmen are well aware of a fact which receives its ex- 

 planation from Sect. III., that every large vessel moving with considerable velo- 

 city sends forward through the ^vater an intimation of its approach while it is 

 yet at a considerable distance, so much as several miles. This intimation consists 

 of a wave or series of waves, propagated in the fluid, with a greater velocity than 

 that of the vessel. A vessel that has ceased its motion, or suddenly varied its 

 velocity, will send forward a very large and defined wave with the velocity due 

 to the depth of the canal, and quite independent of its o^vn velocity. These waves 

 arrive at the place to which the vessel is moving long before she reaches it, and 

 sensibly increase the depth of the water in the channel. I have in this way ob- 

 served on the River Clyde the approach of a large steam-vessel, while yet at the 

 distance of '2k miles, the motion of the wave finding a beautiful index in the oscil- 

 lations of the tall masts of vessels at anchor as it passed them in successive tiers. 

 I have frequently been surprised by the appearance of such an indication, when 

 I had no reason to suspect the approach of a vessel, and have invariably found it 

 followed by the unexpected vessel. A distant storm in the ocean frequently gives 



