TOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 213 



moved from their course by the unusual action, and proves this to be very different 



from flexion *. 



From ail these observations this conclusion follows : that the remarkable pheno- 

 menon in question arises from an action very different from either refraction or 

 flexion ; and whose nature well deserves to be further considered. It may possibly 

 belong to the particles of Iceland crystal, and in a degree to those of rock crystal, 

 from the form and angles of the rhomboidal masses, of which these bodies are 

 composed. Nor is this conjecture at all disproved by the fact, that glass shaped 

 like these bodies wants the property ; for we cannot mould the particles of glass, 

 we can only shape large masses of these ; whereas we cannot doubt that in crystal- 

 lization the smallest masses assume the same form with the largest : but then other 

 hypotheses may perhaps also account for the fact, such as atmospheres, electric 

 fluid, &c. &c. ; so that till further observations are made, we ought to rest content- 

 ed with barely suggesting the query. In the mean time, reserving to a future op- 

 portunity some inquiries concerning the chemical properties of light, and the nature 

 of the forces which bodies exert on it internally, I conclude at present with a short 

 summary of propositions. But first, may I be permitted to express a hope, that 

 what has been already attempted may prove acceptable to such as love to admire 

 the beautiful regularity of nature, or more particularly to trace her operations, as 

 exhibited in one of the most pleasing, most important, and most unerring walks of 

 physical science. 



Prop. 1. The sun's light consists of parts which differ in degree of refrangity, reflexity, Inflexity, and 

 deflexity ; and the rays which are most flexible have also the greatest refrangity, reflexity, and flexity ; 

 or are most refrangile, reflexile, and flexile. — Prop. 2. Rays of compound light passing through the 

 spheres of flexion and falling on the bending body, are not separated by their flexibility, either in their 

 approach to, or return from the body. — Prop. 3. The colours of thin and those of thick plates are pre- 

 cisely of the same nature ; differing only in the thickness of the plate which forms them. — Prop. 4. 

 The colours of plates are caused by flexion, and may be produced without any transmission whatever. — 

 Prop. 5. All the consequences deducible from the theory a priori are found to follow in fact. — Prop. 

 6. The common fringes by flexion, called hitherto the " 3 fringes," are found to be as numerous as the 

 others. — Prop. 7. The unusual image by Iceland crystal is caused by some power inherent in its particles, 

 different from refraction, reflexion, and flexion. — Prop. 8. This power resembles refraction in its degree 

 of action on different rays ; but it resembles flexion within the body, in not taking place at a distance 

 from it j in acting as well on perpendicular as on oblique rays ; and in its sphere or space of exertion 

 moving with the particles which it attends. 



XVI I. On Gouty and Urinary Concretions. By IV. Hyde IVollaston, M. D., 



F. R. S. p. 386. ' 



If in any case a chemical knowledge of the effects of diseases will assist us in 

 the cure of them, in none does it seem more likely to be of service than in the 

 removal of the several concretions that are formed in various parts of the body. 

 Of these, one species from the bladder has been thoroughly examined by Scheele^ 

 who found it to consist almost entirely of a peculiar concrete acid, which, since his 



* When a candle or line is viewed through a deep specimen, the unusual image is tinged with colours. 

 — Orig. 



