91 



mensurable. For instance, the curve, Fig. 2, drawn with powers 3 

 and 2 respectively, give the proper form for a refracting surface of 

 glass, whose index of refraction is 1*50, in order that rays diverging 

 from / may be refracted to F. 



As to the higher classes of curves with three or more focal points, 

 we cannot at present invest them with equally clear and curious 

 physical properties, but the method of drawing a curve by so 

 simple a contrivance, which shall satisfy the condition 

 mr + ni^-\-pr" + &c. = constant, 

 is in itself not a little interesting ; and if we regard, with Mr Max- 

 well, the ovals above described, as the limiting case of the others by 

 the coalescence of two or more foci, we have a farther generaliza- 

 tion of the same kind as that so highly commended by Montucla,* 

 by which Descai-tes elucidated the conic sections as particular cases 

 of his oval curves. 



2. On the Influence of Contractions of Muscles on the Circu- 

 lation of the Blood. By Dr "Wardrop. 



In this paper, Dr Wardrope states that he has endeavoured to 

 shew, by a series of observations and experiments, that the muscles, 

 besides being the active organs of motion, pei'form, by their contrac- 

 tions, an important office in the circulation of the arterial as well as 

 • venous blood ; an oflfice which has not hitherto been described by 

 physiologists, but which appears to be capable of explaining several 

 interesting phenomena in the living body, of which no satisfactory 

 account has yet been given. 



3. On the Solubility of Fluoride of Calcium in Water, and 

 the relation of this property to the occurrence of that 

 Substance in Minerals, and in recent and Fossil Plants 

 and Animals. By Dr G. "Wilson. 



After a preliminary reference to the existence of fluorine in recent 

 and fossil bones, Dr Wilson stated that he had made a series of ex- 

 periments with a view to discover what solvent carried fluoride of 

 calcium into the tissues of plants and animals. Ilis first trials were 

 made with carbonic acid, which was passed in a current through 

 water containing pure fluor-spar in fine powder suspended in it. The 

 fluor was by this treatment dissolved, yielding a solution which pre- 

 cipitated oxalate of ammonia, and when evaporated left a residue 



* Histoire des Mathcmntiques. First Edit. II., 102. 



