ON WAVES. 



359 



In the diagrams, Plate LIV., the waves are laid down from the line A A, and 

 at horizontal intervals of one-tenth of an inch, corresponding to the relative 

 positions of the points at which they were observed. In figs. I and % an ap- 

 proximate mean is given of the waves generated in the large and small chan- 

 nels, each line at the bar A indicating a height of one-tenth part of an inch. 



This table shows in column B, how the height of the wave diminishes as 

 it spreads out from the line of original direction in which it was generated. 

 Lateral diffusion therefore takes place, but with a great diminution of height 

 of the wave. 



This phsenomenon is of importance in reference especially to the law of 

 diffusion of the tides, in such situations as where they enter the German Sea 

 through the English Channel, and the Irish Sea through St. George's Chan- 

 nel. It enables us to account for the great inequality of tides in the same 

 locality. It likewise furnishes an analogy by which we may explain some of 

 the hitherto anomalous phsenomena of sound. 



Axis of Maximum Displacement of the Wave of the First Order. — That 

 a wave of the first order, on entering a large sheet of water, does not diffuse 

 itself equally in all directions around the place of disturbance (as do the waves 

 of the second order produced by a stone dropped in a placid lake), but that 

 there is in one direction an axis along which it maintains the greatest height, 

 has the widest range of translation, and travels with greatest velocity, viz. 

 in the direction of the original propagation as it emerged from the generating 

 reservoir, is a phenomenon which I have further confirmed by a number of 

 experiments. This phaenomenon is of importance, especially if Me take the 

 wave of the first order, the same (as I think I have established) as type of the 

 tide wave of the sea and of the sound wave of the atmosphere. I determined 

 this in the simplest svay. I filled a reservoir which has a smooth flat bottom 

 and perpendicular sides some 20 feet square, to a depth of 4 inches with water. 

 In a small generating reservoir only a foot wide, I generated a wave of the 

 first order. A circle was drawn on the bottom of the large basin, and of 

 course visible through the water, having its centre at the place of disturbance, 

 and divided into arcs of 30°, 45°, 60° and 90°, on which observers were 

 placed, and the heights of the same wave, as observed at the points, is given 

 in the accompanying table. 



