Vision and Definition under the Microscope. 175 



The Authors desire to record their great indebtedness to 

 Mr. Thomas H. Court for his invaluable assistance, both in 

 preparing the instruments for exliibition and in the preparation 

 of this Paper ; to Mr. Charles Lees Curties for adjusting and 

 cleaning the instruments ; and to Mr. Arthur Earland for mounting 

 the objects exhibited. 



