CANADA PORCUPINE 



35 



with the mean variation in each group. To obtain the column 

 at the right, the other columns were combined horizontally by 

 finding the average of the averages for the first, second, third, 

 etc., groups of the first four devices and two combinations, 

 together with the average mean variation corresponding to the 

 same groups. 



700 



SO 



LO 



liO. 



20 



'<B 



?L/\TE I 



A- a— 0-0 Ti^rne \r\ Seconds CTu,os) 



20 



ii.0 



