370 REPORT — 1844. 



oscillations has been transferred along in the direction of transmission with a 

 velocity comparatively slower ; but I have not been able to measure this 

 velocity of propagation of the wave motion from one place to another. 



We have already seen that the velocity assigned by Mr. Kelland and Mr. 

 Airy falls much short of that of the wave of the first order, to which they 

 have thought their results were to be applied. Their results are much nearer 

 to that of the secondary wave, so that it may be questioned whether they 

 should not have applied their results to that rather than the other. Thus 

 by comparing Table XXI. with Table XVIII., it will be found that while the 

 velocity of a wave of the first order, about 6 feet long, is from 5-5 to 8 feet per 

 second, according to the height, that of a wave of the second order is only 

 4-62 feet, which is much nearer to their results. There remains however 

 this difficulty, that high and low waves of the second order of equal length 

 have equal velocities. 



On Observations of the Waves of the Sea. — The chief difficulty in obtain- 

 ing accurate measures of sea waves consists in this fact, that the surface is 

 seldom covered with a uniform series of equidistant equal Avaves, but with 

 several simultaneous groups of different magnitude or in different directions. 

 If there exist more groups than one, the resulting apparent motion of the 

 surface will be extremely different from the motion of either, and may be 

 apparently in an opposite direction from that of the actual motion of the in- 

 dividual series themselves. 



Besides the coexistence of different series of waves, we have the difficulty 

 arising from the fact already mentioned, that a difference exists between the 

 velocity of transmission and the velocity of propagation. From this it results, 

 that after the eye has followed the apparent ridge of a wave, moving with a 

 given velocity of transmission, it will outrun the velocity of propagation, 

 and the wave will appear to cease. This I have continually observed at sea. 

 The eye follows a large wave and suddenly it ceases to pass on, but on look- 

 ing back we find it making once more an appearance on the same ground 

 along which we formerly traced its ridge ; this arises from the cause just 

 mentioned. 



But there are still many occasions on which tolerable observations may be 

 made, and the best will be such as are least complicated by separate systems. 

 The best observations of this kind I have been able to obtain were made for 

 the Committee of the British Association, by the Queen's Harbour-master at 

 Plymouth, William Walker, Esq., who has paid much attention to this sub- 

 ject. He observed the waves as they traversed a space of about half a mile, 

 between two buoys, noting the time of passing, and also the number of waves 

 in the distance between the buoys, whose distance was accurately known. 

 He remarks that in counting the number of waves, great difficulty was found 

 in following a single wave along this space. In fact, as we have already 

 shown, a wave will be often found to fall behind its expected place. 



The resulting velocities got from Mr. Walker's experiments are very 

 various. But on taking out of the. others all those which are mentioned by 

 Mr. Walker as having causes of uncertaintj', I found those which remained 

 very close to those given in Table XXI. 



The following is the Table of observations on sea waves. 



Distance traversed about half a mile ; depth 40 to 50 feet. 



