1818.] Proceedings of Philosophical Societies. 451 



eacli other, and unite in long strings when deprived of their 

 colouring matter. Blood, he says, contains carbonic acid gas. 

 This gas, after the coagulation, endeavours to make its escape, 

 and in this endeavour renders the coagulated blood vascular by 

 drilling channels through it in every direction. Has the author 

 of this hypothesis made any observations to determine whether 

 the globules all disappear when the blood coagulates ? If they do 

 not, where is the proof that the muscular fibres are composed of 

 the white globules ? 



XII. Some Additions to the Croonian Lectwe on the Changes 

 the Blood undergoes in the Act of Coagulation. By Sir E. Home, 

 Bart. — One object of this appendix is to state the real diameter 

 of a globule of the blood as measured by Capt. Kater and Dr. 

 Wollaston. These gentlemen made it at an average -5-oVori 1 of 

 an inch. Another object is to explain in what way it is possible 

 for carbonic acid gas, by its efforts to escape, to render coagulated 

 blood vascular. I have read over this explanation, but cannot 

 say that I understand it, or that I have been able to form to 

 myself an idea of the mechanism of the process. 



XIII. On the Laivs of Polarisation arid Double Refraction in 

 regularly crystallized Bodies. By David Brewster, LL.D. F.R.S. 

 Lond. and Edin. — This is a very curious and valuable paper ; 

 though scarcely of a nature to be rendered intelligible without 

 figures. The author has examined all the crystals which he has 

 been able to procure, and has found no fewer than 165 species 

 capable of refracting doubly. He shows that Biot's division of 

 doubly refracting crystals into positive and negative is merely 

 hypothetical. Some crystals have only one axis of polarisation, 

 some two, and some three. This numfcer of axes is connected 

 with the primitive form of the crystals. All those having one 

 axis have for their primitive form the regular six-sided prism, a 

 rhomboid with an obtuse summit, or an octahedron in which the 

 pyramids have a square base. All the crystals with three axes 

 have the cube, the regular octahedron, or the rhomboidal dode- 

 cahedron, for the primitive form ; while all the other primitive 

 forms belong to crystals having two axes. I shall in a subsequent 

 number of the Annals of Philosophy give a list of the crystals 

 which Dr. Brewster found to refract doubly, and one or two 

 other particulars contained in this paper which may be useful to 

 the mineralogist. At present we have not room to spare for these 

 particulars. 



Article VIII. 



Proceedings of Philosophical Societies. 



ROYAL SOCIETY. 



Nov. 5. — The Croonian lecture was read by Sir EverardHome. 

 The subject was the conversion of pus into granulations of nevr 



2f2 



