TtLASgow society of field naturalists. 209 



He also exhibited a number of rare fungi, e.g., Sphaeria parclalota, 

 S. sfrigosa, S. aqiiila, Ladarms acris, L. rufus, Cantharellus lohatus, 

 C. iphmformis, and Russula sardonia, which he had gathered in the 

 Botanic Gardens, and an immense specimen of Polyj^orus giganfeus 

 from India. 



PAPER READ. 



Mr. Adolph Schulze read a paper on the resolution of test objects 

 for the highest power of the microscope, and stated at the outset 

 that test objects for the microscope were such microscopical objects 

 which require for the revelation of their outlines, their surface- 

 markings, or their internal structure, objectives which possess either 

 or all the essential good qualities of a high class lens. After 

 explaining that for different purposes object glasses of different 

 capacities, and generally of different angles of aperture are required, 

 he noticed the limit of microscopical vision, which according to 

 Hemholtz and Abbe was at half a wave length of that light used for 

 the illumination of the object, so that for violet light, the limit of 

 microscopical vision with perfect glasses would be 115,000 lines per 

 inch. It appeared, however, that in these theories certain properties 

 of light had not been taken sufficiently into account, as it had been 

 demonstrated that lines far closer than the xyjvo ott ^^ ^^ ^^^^ ^^^ 

 been seen by several of our best observers. The physiological limit 

 of microscopical vision is fortunately wide enough to allow of the 

 complete exhaustion of the optical limit. 



The value and use of monochromatic, especially of blue and 

 violet light, for the resolution of the closest lines, was next referred to, 

 as well as microphotography as the greatest aid for demonstrating 

 the markings on the most difficult tests. The importance of a 

 careful correction of the object glass for different thicknesses of 

 covering glass and different mounting media was next insisted upon. 

 The second part of the paper treated of microscopical illumination, 

 and the various methods to obtain such under the highest powers of 

 the microscope. After the lecture he exhibited a number of 

 beautiful objects under one of the highest object glasses yet 

 manufactured, namely, one fiftieth of an inch. 



