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TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



small. This is to be expected, of course, but it should be 

 noted that the greater the number of hauls in one period, the 

 greater is what one may call the " chance " of getting an 

 exceptional result — just by accident. Some method of 

 finding an average which will not be unduly affected by one 

 or two big hauls must, therefore, be found. 



If we take three yearly groups thus, 1892-3-4, 1893-4-5, 

 1804-5-6, etc., and then tabulate the individual hauls in 

 order of their magnitude, we obtain such a table as the 



following one : 



1892-3-4. Fish Trawl. 



No. of Plaice Caught 







per haul. 



Frequency. 



Summed Frequency. 



0-50 



13 



37 



51-100 



6 



24 



101-150 



1 



18 



151-200 



2 



17 



201-250 



3 



15 



251-300 



2 



12 



301-350 



3 



10 



351-400 



2 



7 



401-450 



2 



5 



451-500 



1 



3 



501-550 



1 



2 



551-600 







1 



601-650 



1 



1 





37 





That is, there were 37 hauls in all during the years 1892-93-94, 

 and all of them caught either no plaice or some. There were 

 24 hauls in which either 51 or more than 51 were caught, 

 18 in which 101 or more than 101 were caught, and so on. 

 These summed frequencies have been graphed by setting off 

 the " numbers of plaice caught per haul " on the horizontal 

 axis and the frequencies of occurrence of these catches on the 

 vertical axis. As a rule, the points so found lie fairly regularly 

 and a J -shaped curve (an exponential) is always obtained. 



