RELATIVE POWER OF DISCRIMINATION. 



143 



optional scale for the ordinates. The connection of the terminal 

 points of the ordinates corresponding to the objectives enables us to 

 compare them inter se, and at the same time to estimate the 

 relative productions of the opticians named. The absolute mag- 

 nitude of D first ' comes into account when dealing with the 

 determination of the ordinate corresponding to the naked eye 

 (amplification 1), and it can easily be imagined for every desired 

 value of D. In the figure, the point o.M. represents the limiting 



FIG. 88. 



value of the diameter of the meshes of 103 mic. given by 

 Otto Mueller, and the point N.S. the minimum observed by us, 

 125 mic. 



What first attracts tho eye in the figure is the striking fact, 

 that the highest curves so much exceed the line representing 

 the naked eye, taking the mean value as decisive. The con- 

 trary assertions, which have been made with regard to the 

 power of discrimination of the naked eye, afford no grounds for 

 questioning this fact. They may be explained by the unequal 

 constitution of different eyes; but they leave our repeated 



