590 HENRY A. EOWLAND 



A special form of grating of great defining power has been invented 

 by Professor Michelson of the University of Chicago, called the 

 ' echelon' spectroscope (see SPECTROSCOPY). It is, however, of very 

 limited application. 



See an article on ' Gratings in Theory and Practice ' in Astronomy 

 and Astro-Physics, XII, p. 129, 1893. 



(H. A. E.) 



