1818.] Remarks on Mr. DanielVs Theory. 124 



Article XL 



Remarks on Mr. DanielVs Theory respecting the Specific Gra- 

 vity of Crystals. In a Letter to the Editor of the Annals 

 of "Philosophy. By Pat. Addle, Esq. 



SIR, 



I am one of those who have always derived considerable plea- 

 sure from philosophical inquiries ; but living in a very retired 

 situation, and having little communication with philosophers, I 

 have no means of becoming acquainted with the progress of 

 scientific discovery except through the medium of the public 

 journals. In Number VII. of the Journal of the Royal Institution, 

 published in October last, I have been surprised and delighted 

 with a very extraordinary, a very ingenious, and, as far as I know, 

 a very novel theory of Mr. Daniell on the specific gravity of 

 crystals. The character of this journal, published under the 

 auspices of so learned a body, and conducted by Professors as 

 eminent for their caution as for their talents, is a sufficient gua- 

 rantee that nothing trivial or absurd will ever be found in its 

 pages, and I entered upon the examination of the theory with 

 the confidence that such authority must naturally inspire. 



The formation of crystals from spherical atoms, as detailed by 

 Dr. Wollaston in the Phil. Trans, had previously attracted my 

 attention ; and though I have lived long enough to know that 

 the convulsion of a frog's leg led to the decomposition of the 

 alkalies, I was not prepared to expect, that the theory of Dr. 

 Wollaston (pretty and amusing I admit) should have been but a 

 link in the great chain of discovery, and should have furnished 

 Mr. Daniell with the foundation of a doctrine that bids fair to 

 overturn most of the received opinions in natural philosophy. 



The theory of Mr. Daniell possesses the characteristic of all 

 great discoveries — simplicity, and cannot be more concisely or 

 more beautifully stated than in his own words. After referring 

 to figures representing a tetrahedral and octohedral pile of balls, 

 both composed of triangular faces, the bases of which are con- 

 stituted of four particles, he says, " The tetrahedron is con- 

 tained by four of these similar and equal planes, and the octohe- 

 dron by eight, so that the whole superficies of the latter is 

 exactly double that of the former. Now it is obvious that solids 

 so constructed must differ in their specific gravities, unless the 

 number of elementary particles in the octohedron be exactly 

 double the number in the tetrahedron ; that is to say, unless 

 the number of atoms in a given space be equal in both arrange- 

 ments. But it will be found that the tetrahedon is composed of 

 20 spheres, and the octohedron of 44, the laUer containing more 

 than double the number of particles under a double surface. The 



