276 MR. T. HEELIS ON OCEAN SWELL. 



springs are capable of yielding this amount. The supply- 

 is perennial, and the springs are probably fed by infiltra- 

 tion from the Churnet. There are several other springs 

 bursting forth from this small area of New Red Conglo- 

 merate. 



XIX. — On Ocean Swell. 

 By Thomas Heelis, Esq., F.R.A.S, 



Read January 27th, 1863. 



Besides the undulatory movements which are impressed 

 upon the surface of the ocean by the winds prevailing at 

 the time and place of observation, which movements are 

 known by the name of waves, there are other undulations 

 met with at sea which merit particular attention and study, 

 and which are distinguished by the name of swell. 



These swells are either regular or confused, according 

 to the causes from which they arise. In some cases the 

 same cause produces a confased and also a regular swell. 



The causes of swell are : — 



The direction impressed upon the undulations of the 

 water by winds blowing for a long time in the same di- 

 rection. 



The existence of a current. This is almost always found 

 to produce a swell running towards a point of the com- 

 pass opposite to that towards which the current is flowing. 

 In log-books the current is always noted as flowing to- 

 wards a point, the swell as running from a point, so that 

 current and swell appear to be of the same name. 



These two descriptions of swell are in their nature re- 

 gular, but that arising from current may be disturbed and 

 become confused when it sets in a direction difllerent from 

 that of the winds prevailing at the time and place of ob- 



