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XLI. On the Molecular Constitution of Crystals. 

 By James D. Dana. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN a communication to your Journal for August last, by Mr. 

 R. T. Forster, the author makes a statement which I beg 

 the privilege of correcting. 



Mr. Forster says, speaking of my views on twin- crystals, 

 published in the American Journal of Science for 1836, that the 

 ideas " were directly borrowed from Sir David Brewster," and 

 that the paper by Sir David, containing his views, " was quoted 

 by Dana in the American Jom-nal of Science, and formed the basis 

 of his investigations, without, however, being acknowledged." 



At the time of this "quoting by Dana" in 1832, I was still 

 in my teens, and for fourteen years afterwards I had no con- 

 nexion with the American Journal, and was not in expectation 

 of any such connexion. Instead of Sir David Brewster's paper 

 forming the basis of my investigations, I had not at that time, 

 culpable though it may appear, perused his paper. The con- 

 clusions were mainly arrived at during a cruise at sea in the 

 years 1833 and 1834, when I had by me only a copy of Phillips's 

 ' INIineralogy,' from the measurements of crystals in which ex- 

 cellent work, not knowing at that time in my solitude what 

 had been done by others, I devised also the Haiiyan method of 

 crystallographic calculation. In my paper, pubhshed in 1836, 

 I cite the opinion of Voltz as to the existence of three axes of 

 attraction in molecules, and obviously do not claim originality 

 on that point, the main one in which the theories agi-ee. In a 

 later paper in the American Journal of Science, 1847, vol. iv. 

 p. 169, on " Cohesion," I have alluded to the observations of 

 Sir David Brewster, and made a citation from his paper. The 

 views I have brought forward are diflferent from his in my regard- 

 ing the axial dimensions of the molecule to be those of the cry- 

 stal, and not a resultant between the pressure from the combining 

 attraction and the dimensions: and on the subject of twin-crystals, 

 I am not yet aware that anything has been written by Sir David. 



1 have the highest admiration for the labours of Sir David 

 Brewster, and on the points of difference, while sustaining my 

 own opinions, would not venture to aflSrm my own correctness, 

 knowing that the subject of molecules is the last that science 

 will clear up. I write, not to make claims of originality, but 

 simply to correct an erroneous statement, and disavow all inten- 

 tional injustice. 



Very respectfully, your obedient Servant, 

 New Haven, Conn., James D. Dana. 



September 15, 1H55. 



Phil. Mag. S. 4. Vol. 10. No. 67. Nov. 1855. Z 



