48 



took place would be able to travel quickly and with little effort. 

 How far tliis is made use of by living creatures is I believe, not 

 known . 



The depth at which crab pots are placed varies with the 

 seasons, and it is a matter of some interest to see how the average 

 movements of the water at the 'sea bottom varies throughout the 

 year. I find for the past year, the curve showing the depth at 

 which the velocity at the bottom was one foot jDcr second is 

 practically parallel to the curve showing the depths at which it 

 is the common practice to place the pots. These latter depths 

 have of course been found by experience to represent the depths 

 at which the crabs are caught best, and it would seem that there 

 is a connection, indirect or direct, between the migration of the 

 crabs and the maximum flow of water on the sea bottom. 



The depths at which crab pots are employed should afford 

 protection at all seasons of the year for the case of waves of 

 normal period, even if these waves become fully developed and 

 break. In the case of sudden squalls, although the period at the 

 commencement is much less than the normal period, this rapidly 

 increases and the waves attain their most dangerous length and 

 height some hours after the commencement. In many cases 

 that have been automatically recorded the most dangerous 

 period has occurred after 18 or 24 hours. 



TABLE IX. 



Depth of Water. Horizontal Motion at Bottom. 



