of certain Crystals. 53 



although in such an arrangement it must be admitted that there 

 may be an equilibrium, it is evidently unstable, and ill adapted 

 to form the basis of any permanent crystal. 



More than three years have now elapsed since a very 

 simple explanation of this difficulty occurred to me. As in 

 the course of that time I had not discovered it to be liable to 

 any crystallographical objection, and as it had appeared satis- 

 factory to various mathematical and philosophical friends to 

 whom I proposed it, I had engaged to make this the subject of 

 the Bakerian Lecture of the present year, hoping that some 

 further speculations, connected with the same theory, might 

 lead to more correct notions than are at present entertained 

 of crystallization in general. 



At the time when I made this engagement, I flattered my- 

 self that the conception might be deserving of attention from 

 its novelty. But I have since found, that it is not altogether 

 so new as I had then supposed it to be ; for by the kindness of 

 a friend, I have been referred to Dr. Hooke's Micrographia,. 

 in which is contained, most clearly, one essential part of the 

 same theory. 



However, since the office of a lecturer is properly to diffuse 

 knowledge already acquired, rather than to make known new 

 discoveries in science, and since these hints of Dr. Hooke have 

 been totally overlooked, from having been thrown out at a 

 time when crystallography, as a branch of science, was wholly 

 unknown, and consequently not applied by him to the extent 

 which they may now admit, I have no hesitation in treating the 

 subject as I had before designed. And when I have so done,, 

 I shall quote the passage from Dr. Hooke, to shew how ex- 

 actly the views which I have taken have, to a certain extent^ 



