94 Mr W. Nicol an the Fluicb 



tween the phenomena of the propagation of sound in liquids, 

 and those observed in the propagation of Hght. 



Observations an the Fluids contained in Crystallized Minerals. 

 By William Nicol, Esq. Lecturer on Natural Philosophy. 

 Communicated by the Author. 



To Professor Jameson. 

 Dear Sir, 



JDeing under the necessity of going into the country, I can- 

 not at present continue the investigation I was engaged in, con- 

 cerning the fluids contained in the cavities of crystallized mine- 

 rals. I shall therefore now give you the result of the observa- 

 tions I have already made. 



About two years ago, when polishing a fragment of a crystal 

 of sulphat of barytes, having a cavity containing a fluid and a 

 small moveable globule of air, a partial rent took place from the 

 surface into the cavity. The consequence was, that the globule of 

 air immediately began to expand, and continued to do so until the 

 whole of the fluid was expelled from the cavity. The fluid did not 

 form a continuous line along the rent, but appeared in the form 

 of three or four distinct globules, one of which was considerably 

 larger than all the rest. After inspecting these globules for some 

 time, and seeing no change in their appearance, the fragment 

 was laid aside. On examining it next day, each globule was 

 found to be a solid crystal, having the primitive form of sul- 

 phate of barytes, namely, a right prism with a rhombic base. 

 The waste by evaporation, if any had taken place, must have 

 been very little, for the crystals seemed to be nearly as large as 

 the globules from which they resulted. 



Some time ago, I found in my cabinet a crystal of sulphat of 

 barytes, containing several cavities, in each of which there was 

 a fluid, and a moveable globule of air. With several of these I 

 have succeeded in getting the fluids to the surface through par- 

 tial rents, in consequence of the expansive foice of the air. The 

 fluid always oozed out in the form of distinct globules, of differ- 

 ent magnitudes, one of which was generally larger than all the 

 rest. The globules, however, from different cavities, assumed 

 different appearances. Those from one cavity, for instance. 



