SUIPIIURET OF LEAD, COPPER, AND ANTIMONY. 229 



could not make them, I was under the necessity of waiting. 

 At length I obtained the Object I wished ; I met with crys- More crystals 

 tals, that I could measure with certainty, and had the satis- of itobumecU 

 faction to find, not only that I could loy before the Royal 

 Society more precise observations respecting the character 

 of the crystallization of this substance, but besides a more 

 complete and interesting series of its varieties of form, and 

 a much more complete mineralogical account of every 

 thing concerning it. I had at the same time the satisfac- 

 tion to find, that the first measures I gave, which were 

 simply taken from the crystals with the instrument, differed 

 from those now established by calculation only in that slight 

 degree, which may be ascribed to the unavoidable want of 

 accuracy in the instrument; a difference amounting only 

 to 30' in one of the three varieties I formerly gave, to 19' 

 in a second, and to nothing at all iu the third. This fact 

 may serve as a proof of the near approach to accuracy 

 obtainable by a little practice in using the instrument 

 alone *. 



I shall now proceed to give a complete account of this 

 substance, pursuing the method I adopted in my treatise 

 on mineralogy, the first two volumes of which are just pub- 

 lished. 



By way of preliminary however T shall observe, that as All substances 

 all substances, beside the explanatory terms chat point out re q uire a » »P- 

 their nature, and which are liable to change with the theory nam e. 

 on which they are founded, require a proper name, invari- 

 able in itself, and fixing their existence among natural 

 substances, I have given this the name of endeUion; which This named 

 avoids the termination in ite, so frequent in the nomencla- endeUion by 

 „ , 1 11 • 1 . , lne author : 



ture of mineral substances, and calls to mind, that the 



first specimens of this substance,' which engaged the at- 

 tention of mineralogists, came from EndeUion, in Corn- 

 wall. 



At the same time I avail myself of this opportunity, to v.-urnonite by 



Jameson. 



* Additional note. Since this paper was written, the mensUr?s ob- 

 tainable by the instrument have acquired much greater precision by Dr. 

 Wollaston's ingenious discovery of the reflective goniometer, a di«cove»-y 

 vl great importance to crystallography. 



testify 



