Mr. Phillips on the Ci^ystalline Foinn of the Gaylnssite. 263 



circle) v m v', to find the hypothenuse ?« v (or true zenith-di- 

 stance of the mark m). 



Were fluids indeed subjected, as we have hitherto sup- 

 posed, to the sole action of gravity, our explanation of the 

 theory of the spirit-level might be considered as complete ; 

 but from the effect of the mutual attraction of glass and the 

 liquid of the level, the figui'e &c. of the bubble, as we shall 

 proceed to demonstrate, must suffer material alterations. 

 [To be continued.] 



I 



LIV. Observations on the Crystalline Fm-m, S^-c. of the Gay- 

 lnssite. By W. Phillips, F.L.S. G.S. S^c* 



N the Ann. de Chim. for March 1826, is inserted an account 

 and analysis of a mineral newly discovered in a natron- 

 lake in Colombia, by M. Boussingault, followed by a descrip- 

 tion of its crystalline forms, by M. Cordier. It appears to be 

 a hydrous carbonate of lime and soda ; consisting of Carbonate 

 of soda 33-96, Carbonate of lime 31-39, Water 32-20, Car- 

 bonic acid 1-45, and Alumine 1-0, according to M. Boussin- 

 o-ault. It has received the name of Gaylussite, in honour of 

 the celebrated French chemist M. Gay-Lussac. 



Five crystals of this substance have been presented to me 

 by my brother, who lately received them from Robert Ste- 

 phenson, a gentleman connected with the establishment of the 

 Columbian Mining Company. One only of these crystals is 

 what may be termed symmetrical in its form, the rest being- 

 elongated and channelled on their surfaces in a very remark- 

 able manner. M. Cordier also appears to have possessed only 

 one regularly-formed crystal ; but as this was not, as he ob- 

 serves, sufficiently bright for the use of the reflective goniome- 

 ter, he was compelled to rely on the common one for the mea- 

 surement of its planes. Mine, on the contrary, is remarkably 

 brilliant, and even transparent : I submitted it therefore to the 

 former instrument, which confirms the most important mea- 

 surements by M. Cordier. 



The primary form adopted by M. Cordier is an irregular 

 octohedron ; but finding, as he observes, that " it is not easy 

 to make it clearly appear how the planes of these crystals re- 

 late to that form as their primary," he has substituted, " as be- 

 ing more simple, and as Haiiy had done in analogous cases, 

 an oblicjue prism." The measurements and cleavages of these 

 crystals have led me to the conclusion, that the primary is in 

 reality an oblique rhombic prism, but of diflerent measure- 



* Comnniiiicatcd by the Author. 



ments 



