OBSERVED OFF THE CAPE OF GOOD HOPE. 433 



The time occupied in the passage of this last set was 

 measured and found to be four minutes. 



Assuming the distance from crest to crest to average 

 300 feet^ this would give a speed of about 20 miles per 

 hour. If the distance be assumed as 350 feet, the speed 

 of the waves measured would be above 23 miles per hour. 



In order to check my estimations of the breadth of the 

 troughs between the wave-crests, I took the opportunity, 

 while the ship was being wore round, to estimate again 

 the distance from crest to crest, and to ascertain as well 

 as I could by the time occupied by a crest in passing from 

 the stern to the bows, the speed of the ship at the time 

 being taken into consideration, the velocity with which 

 the crests travel. 



I am pretty sure that the distance between the crests 

 lay between 300 and 350 feet. The speed of the ship 

 being about 3 knots, I found that a wave took 8 seconds 

 in passing from one end of the ship to the other, her 

 length being 200 feet. This will give a speed of about 16 

 knots, or nearly 20 statute miles per hour, agreeing suffi- 

 ciently well (the difficulty of the observation being taken 

 into account) with the speed computed on the estimation 

 of the distance between the crests being 300 feet. 



In the above sets no waves were noted as large which 

 were not estimated as having an altitude of 25 feet or up- 

 wards. The small ones were about 16 and 18 feet, and 

 the very large ones 30 to 34 feet of solid water, no broken 

 crests being measured. The force of the wind at the time 

 of observation was about 8 of the Beaufort scale. It had 

 been blowing 10. 



A wave begins as a small one, gradually increases in 

 height and bulk, and in its onward progress grows in mag- 

 nitude until it attains an altitude at which the crest topples 

 over in foam. From this point it decreases rapidly, and 

 soon ceases to exist, its place being taken by the succeeding 



