764 
wave, it will afterwards be overtaken by the posterior boundary of 
the wave, which. will then leave the fluid particle behind and at 
rest. Thus, at any proposed point, the current will begin when the 
front of the wave reaches that point, will increase there till the 
highest part of the wave is directly over it, and will then gradually 
decrease till the posterior boundary of the wave has reached the 
point in question, where the current will then cease altogether. 
There will be no reflexzon of this great solitary wave unless it meet 
with some obstruction in the course of its motion. 
We are indebted to Mr. Russel for our knowledge of the pro- 
perties of these great waves of translation. He has further ascer- 
tained, experimentally, that the velocity of the wave is equal to that 
which would be acquired in vacuum by a stone falling under the 
action of gravity through a height equal to half the depth of the 
ocean measured from the crest of the wave. He has also found 
that the velocity of the current at any point is independent of the 
depth of that point, being the same at the bottom as at the surface*. 
rom these data it is easy to calculate the velocity of the current 
which attends the wave, when the depth of the ocean and original 
- height of the wave are known. And hence it appears that there is 
no difficulty im accounting for a current of twenty-five or thirty 
miles an hour, if we allow of paroxysmal elevations+ of from 100 
to 200 feet. This velocity will decrease as the wave expands, 
uniess the current be constrained to pass through a comparatively 
narrow channel, like that which must have been formed by the pass 
Stainmoor when just submerged beneath the surface of ‘the ocean. 
In such case the velocity of the current might be much increased. 
With respect to the magnitude of the blocks which might be 
moved by a current of given velocity, the author remarks, that the 
facility with which the transport of a block may be effected 
depends principally on its form. The more it approximates to per- 
fect sphericity, the less, ecterts paribus, will be the force necessary 
to remove it. The author conceives that there is no doubt whiat- 
ever but that blocks, not more spherical than many rolled blocks are 
observed to be, of five tons weight and upwards, might’ be moved 
under favourable circumstances, by a current of ten miles an hour. 
That the force of a current increases in the ratio of the square of 
its velocity has been distinctly established by experiment for all 
velocities up to eleven or twelve miles an hour; nor does there 
* Mr. Russel’s experiments were made with much smaller waves and at 
much smaller depths than those above spoken or ; but he expresses a con- 
viction (and, as the author conceives, a well-founded conviction) that the 
same results will hold for much greater depths than those experimented 
with. Cs 
+ If the extent of country elevated be considerable (like that of the 
district of the Lakes, for instance) the elevation might occupy several 
minutes and still produce the great wave above described. If the elevation 
were produced more slowly, the height of the wave, and consequently the 
velocity of the current, would be proportionably less. 
