PAPER BY PROF. HELMHOLTZ. 129 



These few observations therefore show a connection between the 

 number of waves per minute and the strength of the wind and even an 

 agreement, at leastiu the order of magnitude. But the numbers of waves 

 are all somewhat smaller than they should be as computed from the 

 strength of the wind on shore and leave us to conclude that a stronger 

 wind must have prevailed in the open sea. They show however also 

 that the re-action of a strong wind may last many days. 



For a progressive velocity of 10 metres the waves would in one day 

 travel 7f degrees of longitude. Therefore, had the Mediterranean even 

 to the Gulf of Sidra been on the 1st of April covered with waves ex- 

 cited by a strong breeze of 10 metres velocity, these would need two and 

 a half days before the last ones would reach the coast of southern 

 France. 



It will of course be possible to solve the problem more thoroughly 

 only when we hav e at hand continuous registers of the billows and ex- 

 tended observations of the velocity of the wind. These latter are un- 

 fortunately not yet collected for the mouth of April of this year, or at 

 least not yet published, and could therefore not be used by me, 

 80 A 9 



