TEST OBJECTS. 



477 



La Rue with another test- plate of fifteen series of lines, which 

 has been resolved as follows : — 



JVoberfs recent Test Plate of 15 series of lines. 



All the foregoing were seen with a quarter inch object- 

 glass of Ross's make, and having an aperture of 80°, the slide 

 being illuminated -in an oblique direction with a common bull's 

 eye. 



In order to render the subject more intelligible, the author, 

 through the kindness of his friend. Dr. J. Hughes Bennett, 

 has been enabled to give the following representations of 

 M. Nobert's truly wonderful productions. Figi 261 exhibits 



a piece of glass of the same size 

 as the original, on which in the 

 centre are ruled the ten bands 

 or clusters of lines before al- 

 luded to, the entire number 

 occupying so small a space as 

 Fig. 261. the one-fourth of a Une; when 



