52 Prof. Potter on the Fourth Law of the Relations of the 



described, occupying precisely the same geological position, in 

 localities so far apart as the counties Carlow and Fermanagh, 

 suggests the possibility of a dolomite horizon, marking the 

 upper limit of the carboniferous limestone of Ireland. 



In the lower parts of the carboniferous limestone of Ireland, 

 where the limestone abuts against the granite of the Leinster 

 chain, dolomites are locally abundant, which differ from the do- 

 lomites of the upper limestone in containing a much larger pro- 

 portion of argil. 



I here give the analyses of two specimens from localities far 

 asunder. 



No. 3. Dolomite from Brown's Hill Quarries near Carlow, 

 within a quarter of a mile of the junction of the limestone and 

 granite ; much used as a building- stone, but known to make bad 

 lime. This dolomite is of a bluish-grey colour, is not crystalline, 

 and contains numerous geodes filled with yellow clay, lined with 

 crystals of Bitter-spar, and containing loose double-pyramidal 

 crystals of quartz, many of which include cavities partially filled 

 with fluid, enclosing small spherical bubbles, which are moveable 

 on changing the position of the crystal. Spec. grav. =2*781. 



Carbonate of lime . 

 Carbonate of magnesia 

 Carbonate of iron 

 Argil 



98-79 

 No. 4. Dolomite from Booterstown, co. Dublin ; within a few 

 yards of the granite which appears at the Black Bock station of 

 the Dublin and Kingstown Railway. Dark grey, not crystalline, 



Per-centage. Atoms. 

 Carbonate of lime . . 47*21 0*944 

 Carbonate of magnesia . 25*64 0'600l n r> nr 

 Carbonate of iron . . 11*89 0-205J U ' 5UJ 

 Argil ....... 15*66 



100*40 



VII. On the Fourth Law of the Relations of the Elastic Force, 

 Density, and Temperature in Gases ; as sequel to a Paper on 

 the same subject in the Philosophical Magazine for September 

 1853. By Professor Potter, A.M.* 



THERE is no need to be surprised that our knowledge of the 

 relations of heat and dense matter has progressed slowly ; 

 for in examining these relations we are striving to learn the con- 

 * Communicated by the Author. 



Per-centage. 



Atoms. 



, 49*84 



0*997 



, 39*36 



0-937 



, 0-99 





. 8-60 





