1818.] respecting the Specific Gravity of Crystals. 127 



my wife, who, good soul, has no enthusiasm in these matters. 

 It occurred to me, however, that if true of fluor spar, it must be 

 equally so of eveiy body in nature, fluid as well as solid. If 

 from the same mass .of fluor spar I "obtain a different specific 

 gravity according as I detach an octohedral or tetrahedral 

 crystal, it follows, that by confining the same fluid in a vessel 

 of an octohedral or a tetrahedral form, I shall so alter the surfaces 

 of the mass of fluid compared with the number of elementary 

 atoms, that its specific gravity must vary with every modification 

 in the form of the vessel which contains it. 



By the help of a' rough model, an intelligent tinman in the 

 neighbouring market-town, constructed for me an octohedral 

 and a tetrahedral vessel, consisting of equal triangular faces, one 

 of which was left open for the purpose of pouring in the fluid. 

 The octohedron held two gallons, for it would have been absurd 

 to risk the success of the experiment by conducting it on a small 

 scale ; and, to say the truth, I abhor (what it has been the 

 fashion of late to call) microscopic chemistry. Besides, the 

 beer can in my servants' hall held exactly two gallons, and to 

 the eye was cylindrical. A large china punch-bowl, in which 

 all my children had been christened, though not perfectly a 

 hemisphere, was so near an approximation that I had no appre- 

 hension of error on that score, and a large kitchen funnel fur- 

 nished me with a cone. The octohedron was laid upon one of 

 its triangular faces, with the open side uppermost, and the tetra- 

 hedron was supported upon its apex in a large mass of clay, so 

 that the plane of the open side should be perfectly horizontal. 

 Thus prepared, I. had the vessels carefully filled with water, all 

 taken from the same pump, and successively plunged a beautiful 

 hydrometer of Nicholson's into the octohedron, tetrahedron, 

 funnel, beer-can, and punch-bowl. Now, Sir, I leave you to 

 judge of my mortification on finding the instrument indicate 

 identically the same specific gravity in all. 



I varied the experiments by using distilled, instead of pump 

 water; I tried Atkins's and Sykes's hydrometer, and the areometer 

 of Beaume, repeatedly, and always with the same result. After 

 recovering from the temporary shock this disappointment occa- 

 sioned, I soon, upon reflection, discovered that the pressure of 

 the fluids upon the sides of the vessels being exactly equivalent 

 to the pressure of the sides upon the fluid, I had no chance of 

 ascertaining the difference of their specific gravities, unless they 

 could be freely retained in their forms by their own specific 

 attractions, and any attempt to obtain them in this state being- 

 hopeless, I abandoned these experiments as anomalies that 

 would be explained when I had time to calculate the necessary 

 allowance for pressure. 



Not long after this, on my return one moonlight night from 

 dining with a neighbour after I hud been thinking of a mode of 



