Eye-pieces for the Microscope. By E. M. Nelson. L49 



In Table II., the figure over the inches column relates to the 

 long tube, and that over the millimetre column to the short tube. 

 Eings are to be placed over the eye-piece tubes to maintain the 

 value of t ; the eye-pieces are therefore " parfocal." As stated 

 previously, " parfocal " eye-pieces were, in 1839, made by Powell, 

 who has continued to make them ever since. It was probably 

 Cornelius Varley who suggested this idea to Powell. 



A correction is needed with regard to the statement in my 

 previous paper that Varley was the first to fit a draw-tube adjust- 

 ment between the eye-lens and the field-lens of the Huyghenian eye- 

 piece, for subsequently, while cleaning a signed Benj. Martin Micro- 

 scope, I discovered a similar draw-tube which clearly pre-dates 

 Varley's design. 



My acknowledgments are due to Mr. W. B. Stokes for correc- 

 tions and useful suggestions. 



