THE JOURNAL 



OF THE 



iielictt ^ttrostapical Chrb. 



On the Resolution of Ampeipleura pellucida, etc., with a 

 Dry Lens and Axial Illumination. 



By a. a. Merlin, F.R.M.S, 



{Read Novemher 16th, 1900.) 



Many members of our Club have been long familiar with the 

 structure of Amphipleura pellucida as revealed by oil-immersion 

 objectives of the highest class and aperture. The point to which 

 I now beg to call your attention is the accomplishment of the 

 resolution of normal specimens of this diatom by means of Zeiss's 

 dry 4 mm. apochromat, and a |ths solid axial cone from Powell's 

 adjustable apochromatic condenser. 



I was led to attack the A. pellucida with the above specified 

 optical arrangement through having remarked the great strength 

 of the resolution yielded by some realgar-mounted specimens 

 under the Zeiss 3 mm. of N.A. 1'4 and a solid axial cone of 

 about N.A. 1*2 from an oil-immersion condenser. I must confess 

 that the exact theoretical resolving limit of an object glass 

 of N.A. '95, as given in the table on page 85 of Carpenter's 

 " The Microscope and its Revelations " (Seventh Edition, Edited 

 by Dallinger, 1891), had at the time escaped my memory, other- 

 wise it is extremely improbable that any such attempt would 

 have been made. 



JouRN. Q. M. C, Series II.— No. 48. 1 



