144 Mr. A. Schuster. Experiments with [June 5, 



Table II continued. 



Nui 



Observer. 



5 

 17 



28 

 50 



72 



16 Colour blind. 

 66 Colourblind. 

 70 Colour blind. 



The first column in the above table gives the number which 

 identifies the observer, the second column the number of readings 

 taken, the third the mean difference between the observer and myself, 

 or Mr. Hadley. The fourth column gives an idea of the consistency 

 of the same observer in reading. It is the mean difference between 

 a single reading and the mean of all the readings, negative differences 

 being counted as positive ones. A glance at the table shows that 

 this mean difference is generally about two or three tenths of a 

 division. 



From the results of column 3, Table III has been obtained. 

 Column II gives the number of observers whose readings do not 

 differ by more than half a unit from the numbers given in column I. 

 Column III gives the mean of three successive values of column II, 

 that row against which the number is placed being the middle of the 

 numbers whose mean is taken. 



Table III. 



Column I. II. III. 



-16 1 07 



-15 1 1-7 



-14 3 1-3 



-13 1-7 



-12 2 1-7 



-11 3 2-3 



-10 2 27 



-9 3 1-7 



-8 2-3 



-7 4 2-0 



-6 2 4-3 



-5 7 57 



-4 7 6-0 



