21 



Matthews to re-consider his judgment. In the case of light converging at 

 an angle of 85°, if they took the thickness of the covering glass and of the 

 stratum of air between, and also the thickness of the film of water into 

 consideration, they would see that light passing at an angle of 85° could 

 not enter the objective at all, but could only be seen as light received by 

 the object and again thrown out by it as its own radiant. They saw an 

 object negatively by virtue of its power of obstructing light, whereas, if they 

 could make it receive light to such a degree as to become its own radiant 

 while no light entered the objective except that given out by the object, he 

 apprehended that it must be seen as a positive image. Here it was seen 

 upon a perfectly black background, the Podura scale appearing as if in- 

 candescent. 



Dr. Matthews said that the principle enunciated by Dr. Edmunds was 

 perfectly correct, but yet he could not see that any object illuminated only 

 from below could afford any other than a negative image when looked at 

 from above — unless light were reflected back upon it from the under surface 

 of the cover. 



Dr. Edmunds feared he had not clearly explained ; no light could come up 

 through the surface of this slide, except into the substance of the object, 

 otherwise they would of course cease to get the black background. 



The President said that the discussion as to positive images opened up a 

 series of complicated questions, which it was clear they could not go into 

 that evening. 



A vote of thanks to Dr. Edmunds for his communication was then unani- 

 mously carried, and the proceedings terminated with the usual conversazione, 

 at which the following objects were exhibited : — 



Section of China rose ... ... ... ... by Mr. F. W. Andrew. 



Spicules of Holothuria ... ... ... ... „ Mr. T. H. Buff ham. 



Anchors of Synapta ... ... ... ... „ Mr. F. Coles. 



Scalariform tissue of Fern ... ... ... „ Mr. A. L. Corbett. 



Podura scale, Lepidocyrtus curvicollis (shown I y. -p, , -, 



by Dr. Edmunds' immersion paraboloid) J 



Strophosonius obesus ... ... ... ... „ Mr. Enock. 



Scylla, from wet moss ... ... ... ... „ Mr. H. E. Freeman. 



Sieve tubes from Dahlia „ Mr. W. H. Gilburt. 



Fin of young Carp „ Mr. Halley. 



Nasal Polypus „ Mr. J. J. Hunter. 



Grammatophora marina ... ... „ Mr. Michael. 



Section of Human Tongue ... ... ... „ Mr. Moginie. 



Amphipleura pellucida (by Dr. Edmunds' > i\r -d m 



r ,, Air. Jrowell. 

 immersion Paraboloid) ... ... * 



Arachnoidiscus ornata ... ... ,, Mr. B. W. Priest. 



Mignonette „ Mr. F. Reeve. 



Polycistinoa „ Mr. Swift. 



Attendance — Members, 86 j Visitors,, 14. 



