OP ARTS AND SCIENCES. 



223 



produced by an increase in the scale-reading equal to the average 

 deviation in inches. 



TABLE II. 



Average deviation I. P. = .004. 



Average deviation I. P = .009. 



Tables III. and IV. give the means of the various sets of experi- 

 ments. Column 1 shows the sample used ; 2, the mean of the 

 series taken ; 3, the number of observations from which the mean is 

 derived ; 4, the observer ; 5, the illuminating power ; 6, the average 

 deviation in inches ; and 7, the average deviation in terms of the illu- 

 minating power. It will be seen that the maximum average deviation 

 in I. P. for the finer wire is 1.7 per cent, and for the coarser wire 1.6 

 per cent of the total value. 



TABLE III. 



Diameter of wire = .004 in. 



