382 PROCEEDoas of the society. 



Tho Presiilcut thought that Dr. Ord's communicatioii was one of 

 remarkable interest, which appeared to open up a new matter for 

 promising investigation, and which he hoped Dr. Ord himself would 

 develope at greater length in a form for publication. 



Mr. T. Charters White mentioned, as bearing upon tho subject, 

 the molecular disturbance which took place on the surface of glass in 

 the case of photographic negatives. 



Dr. Matthews said there were certain kinds of glass which 

 appeared to undergo spontaneous decomposition ; this was particu- 

 larly noticed in the case of the very old glass found in tombs and 

 causing the iridescence. 



Dr. G. D. Brown said that a somew-hat similar effect had been 

 observed in the case of old glass in windows ; particularly thoso 

 which faced the south-west. 



Prof. Stewart thought that tho disintegration of glass which was 

 the cause of the colours referred to, belonged to a different category, 

 as indicated by Sir David Brewster in a paj^er which he published 

 upon the subject. In examining decomposed glass the primitive 

 surface might often be observed to be broken up into concentric films, 

 frequently following definite lines. When this layer breaks off it 

 leaves the surface pitted with spheroidal depressions. There were, he 

 thought, some difiicultics to meet in endeavouring to account for all 

 the phenomena by molecular movement, as, for instance, in the case 

 of Eydractinia arhorcscens, where a film of chitin separated the proto- 

 plasm of the organism from tho incnisted shell. As regarded tho 

 boring powers of certain sponges and the removal of lime, he thought 

 that the suggestion of Dr. Ord was very likely to be correct, and that 

 the movement of the heavy molecules of the colloids might, sledge- 

 hammer-like, increase the motion of the molecules of the body acted 

 upon, and finally produce the observed effects. 



Mr. Cheshire thought that there was a curious mathematical side 

 to this question as bearing upon the velocity imparted by the stroke 

 between the heavy molecule of the colloid and the lighter molecule of 

 the lime. 



Dr. Ord replied to the remarks that had been made, and exhibited 

 a specimen and also enlarged diagrams of a sjihcroidal calculus of uric 

 acid, found in the kidney of a patient, surrounded by a layer of a 

 chitinoid nature, and showing extensive erosion of the uric-acid 

 nucleus by its colloid investment. 



Prof. Stewart mentioned a case of the peculiarly resistent substance 

 of oxalate of lime calculi being similarly eroded. 



Mr. J. W. Stephenson read his paper " On a New Cata-dioptric 

 Illuminator," having an aperture exceeding that of any existing 

 objective — or equal to 1-644 N.A. in flint glass, and 1-512 N.A. in 

 crown glass. The subject was illustrated by diagrams and by tho 

 exhibition of the apparatus {supra, p. 207).^ 



The President thought that all who were in the habit of using 

 high-angled lenses would feel indebted to Mr. Stephenson for giving 



