/. D. Dana on Cohesive Attraction. 369 



kneaded together like a soft gum or jelly." He concludes from 

 the facts, that the topaz must have been in a soft and plastic state 

 while it yielded to the compressing force which emanated from 

 the cavities, and farther, infers (as in 1805 from his experiments 

 on depolarization) " the existence of a new species of crystalliza- 

 tion, which is the effect of time alone, and which is produced 

 by the slow action of corpuscular forces." 



If the facts prove a comparatively soft state of the topaz when 

 first formed, as they appear to do, they indicate that the crystal 

 while afterwards hardening, would undergo contraction, in which 

 case such minute cavities or any foreign particle would become 

 apparent centres of a compressing force. The regular form of 

 the topaz crystal, presenting a perfect correspondence in every 

 respect with other crystals, can be explained only on the sup- 

 position of axial attraction ; and while the necessity of time and 

 corpuscular forces must be admitted, we fail to see evidence of a 

 new species of crystallization. In the diamond, the same prin- 

 ciple may have operated. If the crystal when first formed is 

 sfill imperfectly hardened, contraction would continue for a 

 time in progress ; and the contraction in this case acting with 

 some reference to radii from the centre, and affecting most the 

 prominent edges and angles, might give the convex form present- 

 ed by the faces of the crystals, and the peculiar structure within. 



The fact mentioned at the meeting of the British Associa- 

 te in June last, by Mr. H. F. Talbot, that a fused globule of 

 nitrate of potash polarized light, like a regular crystal, only 

 shows that some species may retain the axial forces and arrange- 

 me nt in the fluid state. It is known that certain fluids have the 

 power of polarization. These facts extend instead of limiting 

 °nr proposition, proving that the molecules of some substances, 

 <*en in the liquid state, may have the inequiaxal forms, generally 

 Elected only in solids* 



"Sir David Brewster, after mentioning his 1^SS^%!tSSVi 

 Peeing the polarizing structure in glass and other Stance .by ten* u 



f ts that the P polarizing .trt.cU.re of crystals ar.ses from the mutual pn ure o 

 *• el^ic particles during crystallization. He conclude, that the ^ ^ry., a. 

 ^t-on are' three in number and at right angles to each " her »nd J ..that 



*"•«» any two molecules are brought together by the fi.roeso ^ nr ^ ,*,„,. 

 *°°uce a crystalline arrangement and strongly adhere, t\ g«" £?£ Section 

 P^s one another, and each will have an ax.s of double refract on ,n , the d 

 f l '»e line joining their centres, in the same manner as if they bad neen P 



* hy an external force." •,..!„ ., n d more in accordance 



J he facts are explained, as we believe : more simpl -and J '' |ariMli , in in 

 *"h the laws of crystals, by attributing the character of ordinary P . . 



Ratals to the form of the molecule independent of t^*** ™ £ af ,ding 

 J" '»> crystals must be inequiaxal and th.s ., a ,,.»hcent rea. on, * tt. ^ g 



£' '<re as an additional ca, Pressure at he tg£™*^ 2to*t with the 



We., and this would make an irregular sol.dof the ellipsoid, incon-wi 



s 'cond SiatEs, Vol. IV, No. 12.— Nov., 1847. 47 



