20S PRIMITIVE CRYSTALS OF SOME CARBONATES. 



VIII. 



On the primitive Crystals of Carbonate of Lime, Bitter-Spar, 

 and Iron Spar. JEC?/ William Hyde Wollaston, M. D. 

 Sec. R. S*. 



Angles of "WIT THEN I formerly described to the Society a goniometerf 

 rected by the ^ ^ "P°^^ ^ ""^w construction for measuring the angles of 

 author's goni- crystals, I expressed an expectation, that we should thereby be 

 •meter, enabled to correct former observations made by means of less 



accurate instruments. I took occasion to mention one instance 

 of inaccurate measurement in the primitive angle of the com- 

 mon carbonate of lime j and I have had the satisfaction to find 

 the necessity of a correction, in that instance, confirmed by 

 Mons, MaJus, and admitted by the Abbe Haiiy, in a work+ 

 published nearly at the same time. 

 Haiiy's accu- It is by no means my design to detract, in any degree, from 



ral^^surprfsinff. ^^'^^'"'^ °^ ^'^^'■i^^'-'y '^*^^^^^^'^'^ ^'T^'^'^°§''^P^^ ^° ^^^ ^^^' 

 prising accuracy of whose measurements I could, in various 



instances, bear testimony. I hope, on the contrary, that in 

 bringing forward two more observations similar to the pre- 

 ceding, and intimately connected with it, I shall offer what 

 will not only appear interesting to crystallographers in general, 

 but will be peculiarly gratifying to the Abbe Haiiy. 

 The same pri- In his Traite de Mineralogie, and again more recently in 

 assiffned°bv^ his Tableau Comparatif, the same primitive form is assigned 

 him to three to three substances very different in their composition to car- 

 substances; bonate of lime, to magnesian carbonate of lime (or bitter-spar) 



and to carbonate of iron. 

 Heatlty of It has been objected to Mons, Haiiy, that according to his 



composition method identity of form should be accompanied by identity of 

 •hould accom- . • , , ^ /- i i 



pany identity composition, unless the form were one of the common regular 



©f figure. solids. For though in this case any geometrician would readily 

 admit it to be very probable, that many different substances 

 might occur in assuming the same form of cube, of octo- 



* Philos. Trans, for 1812, p. 159. 



f Philos. Trans, 1809, p, 253 ; or Journal, vol. XXV, p, 192. 

 i Tableau Comparatif de» Resultats de la Crystallographie et de 1' Ana- 

 lyse Chimiq^ue. 



% hedron. 



