85 THEORIES OF CRYSTAtLOOR A PHY. 



Laws of the When fpeaking of the approach of the proper particles, I 



fr "fSir^aid ^^'^ ^^^^ '^ might be occafioned by the fubtradion of certain 

 theory thence interpofed particles which obftruded the approach of the pro- 

 rcfulting, p^j. particles. The former are generally water, caloric, or 



any fluid elallic or not. Their exit may perhaps make place 

 for others, fuch as light, eledlricity, &c, &c. ButtheeflTen- 

 tial point is, that whatever thefe particles may be, they are 

 in perfe6t equilibrio with the proper particles, otherwife they 

 would become perturbing forces. Hence it follows, that not 

 only the integrant particles of the cryftal, but all thofe that 

 are mixed with them, the chemical or component particles 

 and even the vacuities, rauft follow the fame laws. It alfo 

 follows, that if each fpecies of particle (even the chemical) 

 that enters into the formation of the cryftal be feparately con- 

 iidered, each fpecies will have its diftind fymmetrical and 

 polyedral form. The forms will penetrate each other, while 

 the particles will not only not penetrate, but not even touch 

 each other. All forms would fland in the fame predicament 

 as the regular odaedron, which contains, as the Abb^ Haiiy 

 has demonftrated, fix regular odtaedrons and eight regular 

 tetraedrons, each tetraedron containing one odaHdron and 

 four tetraedrons. It will further follow, if the chemical ele- 

 ments can be looked upon as particles which are not in con- 

 - tact with each other, that we may from thence mathematically 

 determine chemical affinities. 



I have now. Sir, but one talk left ; to fpeak of the appli- 

 cation our author has made of algebra and geometry to cryf- 

 tallography. Many perfons complain of the difficulty nccef- 

 farily refulting from it in the ftudy of mineralogy ; and dare 

 not engage in it, uncertain whether they will find a compen- 

 fation for their trouble. Our author has therefore adopted a 

 double plan, and begins by expofing his theory by a feries of 

 reafonings and arguments which will fuffice to make the reader 

 underftand it, or any difcoveries made in confequence of it. 

 He then expofes the theory in the moft corred of all languages 

 — mathematical analyfis ; by far the mod interefting, and the 

 only means of making difcoveries oneVfelf : and who can be 

 caHous to the pleafure of difcovering an unknown truth ? If 

 the folution of a problem gives fo much fatisfadion, though 

 thei data be only imaginary, what mufl be the fenfations of 

 thofe who are happy enough to folve problems whofe data are 



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