436 ON THE HEIGHT AND ORDER OF SUCCESSION OF WAVES. 



tion, yet I am convinced that the speed of waves in mo- 

 derate weather does vary. When a wave has overtaken 

 that which precedes it^ it will unite with it, and assist in 

 producing the difference of height so often observed. 



In some of the cases observed on the i8th July, the 

 speed but slightly exceeds that of the waves measured on 

 the 13th of the same month, although the force of the 

 wind on the 13th was nearly double that of the wind on 

 the 1 8th, the difference between the forces of the wind 

 denoted by the successive numbers near the end of the 

 Beaufort scale being much greater than those between the 

 lower numbers, 



The question suggested by the Admiralty ^Manual of 

 Scientific Inquiry,^ whether the height and distance of the 

 ridges vary with the velocity, can best be solved by com- 

 parison of distinct series of observations, taken at different 

 times, in or near the same locality, as it is hardly capable 

 of distinct observation contemporaneously with other points 

 of inquiry. 



The above remarks are independent of the question 

 whether, in addition to the series of undulations measured, 

 there be not (as circumstances seem to prove that there 

 are) series of undulations which take a longer time than 

 those measured, but which coincide with them at certain 

 longer intervals. During a gale of wind, two or three 

 very large waves will often come together at intervals of 

 ten minutes or a quarter of an hour, or sometimes at even 

 longer intervals, causing the ship to lurch fearfully ; but 

 no observations yet made have ever reduced these to any 

 known system or series of undulations. 



My observations show that, beyond a certain point, the 

 force of the wind has very little influence in increasing the 

 speed of waves. I do not think that they often run much 

 beyond 25 miles per hour. 



