162 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



N.B. — Since the above paper was read, the author 

 of it has gained additional experience in the use of 

 these apochromatic objectives which fully bears out 

 the high opinion he formed of them when first he 

 began to employ them. Above all would he recom- 

 mend them when the best possible definition is 

 required, and, especially in conjunction with the 

 projection eyepieces, for photo-micrography, as in 

 consequence of the coincidence of their visual and 

 actinic foci the operator can with certainty obtain 

 a sharp image on the sensitized plate. 



Dr. Roderick Zeiss, of Jena, has succeeded in photo- 

 graphing even the longitudinal lines on Amphipleuva 

 pellucida with one of Zeiss' homogeneous apochro- 

 matic objectives of 2 mm. focus and of only 1'30 

 mm. aperture — a feat which has not been accom- 

 plished hitherto with any other lens of the same 

 aperture. Numerous imitations of these lenses have 

 been placed of late in the markets, and some no 

 doubt of excellent quality and great resolving power, 

 but, so far as the author has been able to learn, 

 none truly apochromatic in the sense in which 

 Professor Abbe has introduced this appellation. 



